Programming: C Basic

C Basic

What is language?

A language is medium in which two or more object/person communicate their thought, information, data etc. C is computer language. Computer languages are generally two types:

1. High Level Language-Translator required must example: FORTRAN

2. Low Level Language-Not requirement translator example: machine language(0 , 1)

C is a high level language with low level programming features so it is also called middle level language i.e. we can write program either in machine language (0 , 1) or general English keyword (HLL).
C is a structured programming language, that is developed by Dennis Ritchie in 1972 at AT & Bell Laboratories in USA.
Some basic tips for C Programs and C language:

1. Each instruction in a C program is written as a separate statement. Therefore, a complete C program would comprise a series of statements.

2. The statement in a program must appear in the same order in which we wish them to be executed, unless the result will be differ as we want wish.

3. All statement are entered in Small case letters.

4. Every C statement must be end with a semicolon (;). This is act that statement has been terminated

5. C is "free form language" i.e. there are no specific rule for where the statement write.

There are some other language like as C++, C# and Java, its languages are more advanced then c, then

Why we learn C today?

There are some reason behind this question that's are following:

1. C is the basic (mother) of all other languages.When you had learned c, you are easily deal with classes, object, template, structure, polymorphic and with familiar terminology.

2. C++, C# and Java are OOP Object Oriented Programming) languages. So when u creating object u must still a good command on C language.

3. Major parts of OS (Operating System) like as Windows, UNIX, and Linux are still written in C.

4. C language is known for owns speed and execution.

5. Today daily routine apparatus like as microwave, washing, digital camera's, microprocessor, and operating system, smart phones are worked in C programs.

6. Maximum 3-d games are built in C.

So now let's start to learn C.

Constant

1. Constant is an entity that does not change during program execution. Example when we write number=10 than 10 is constant in all program and never change value.

2. There are mainly two types constants:

1. Primary constants

§ Integer constant

§ Real Constant

§ character Constant

2. Secondary Constants

§ Array

§ Structure

§ Pointer

§ Union

Rules for construction Integer Constant

At least one digit must have an integer constant
It can be positive or negative. The general range of integer constant is -32768 to +32767. (NOTE : Normally range depend on compiler.)
No commas or blank spaces are allowed within integer constant.
Integer constant must not having decimal point.
Example of integer constant are as 364,-66,+786,-1

Rules for constructing Floating point or Real constant

At least one digit must have an real constant.
Real constant must have decimal point.
It may be positive or negative.
No commas or blank spaces are allowed within real constant.
Example of real point constant : +23.0, 786.786, -0.786, 0.0

Rules for constructing Character constant

Any single entity(like as single alphabet, single digit or single symbol) are enclosed within single inverted commas, are called character constant.
Example of Character constant : 'a', 'A', '*', '4' etc..

Variable

Variable

1. Variable is an entity that change during program execution. Example when we write r = 45 i.e. x can hold different value at different times so r is a variable.

2. A variable may be integer, character, float, double etc..

Rules for constructing Variable Names:

A variable name must be start with alphabet or underscore.
A variable name is any combination of 1 to 31 alphabets, digits or underscores.
No commas, special symbol(rather than underscore [ _ ] ) or blanks are allowed within a variable name
Example of valid variable names : ram, _ram, d_x, _voids, echo_,

Keywords in C

C keywords

Keywords are standard word whose meaning has already been explained to the compiler.
Keywords are also called "reserved words".
There are 32 keywords available in C.

int	char	long	double	float	break
continue	goto	void	switch	case	default
short	signed	unsigned	if	else	for
while	auto	register	static	extern	do
const	enum	return	sizeof	struct	typedef
union	volatile

Data type in C

Data Type in C Language

There are mainly three data type in C as following:

1. Basic Data Type

o int

o char

o float

o long

o double

o long double

2. Derived Data Type

o Array

o Pointer

o function

3. User Define Data Type

o structure

o union

o enumerated

o typedef

Following table tell which data type how much allocate memory?

Data Type	Memory Allocation
int	2 byte
long	4 byte
float	4 byte
double	8 byte
long double	10 byte
char	1 byte

In data types we also learn about link list, file handling and more. So now we are entering in real c world i.e. C programming.

Compilation and execution of programs

Compilation and execution

There are many steps involved in converting a C program into an executable form, these all steps are called "build process".
Build process are representing in the following graphically diagram :

C Source code Programs (assume file name first.c)

Expanded source code (first.i)

Assembly code (first.asm)

Relocatable Object code + Object code of library function

Executable code (first.exe)

Figure: Build process

If you don't understand the build process, don't worry, read following explanations of build process i.e. how a source program make executable program. It is all internal process of machine, that's done in neon seconds.

Let’s now understand the steps mentioned in above figure in detail.

1. Editor-Type your program in editor (source code).

2. Preprocessing-During this step, the C source code is expanded based on the preprocessor directives like as #include, #ifdef, #define etc. The expanded source code is stored in an intermediate file with .i extension.

3. Compilation- The expanded source code is then passed to the compiler, which identifies the syntax error in the expanded source code. If the expanded source code is error free, then the compiler transfer the expanded source code in C, into an equivalent assembly language program. The assembly code is typically stored in .ASM file. So our first.c file would be changed and stored in first.ASM.

4. Assembling - Assembler translate the .ASM program into Relocatable Object code. Thus assembler translate our first.asm file into first.OBJ. .OBJ file is one of the binary file. This object file contained header and several section.

5. Linking - Linking is the final step of build process i.e. creating an executable program. It's do following works :

o Find definition of all external function

o Find definition of all global variables

o Combine Data Section

o Combine Code Section

6. Loading - Once the .EXE file is created and stored on the disk, it is ready for execution. When we execute it, it is first brought from the disk into the memory (RAM) by an OS component called Program Loader.

Algorithms and Flowchart

Algorithms

1. A sequential solution of any program that written in human language, called algorithm.

2. Algorithm is first step of the solution process, after the analysis of problem, programmer write the algorithm of that problem.

3. Example of Algorithms:

Q. Write an algorithm to find out number is odd or even?

Ans.

Step 1: start

Step 2: input number

Step 3: rem=number mod 2

Step 4: if rem=0 then

print "number even"

else

print "number odd"

endif

Step 5: stop

Flowchart

1. Graphical representation of any program is called flowchart.
2. There are some standard graphics that are used in flowchart as following:

Figure: Start/Stop terminal box

Figure: Input/output box

Figure: Process/Instruction box

Figure: Lines or Arrows

Figure: Decision box

Figure: Connector box

Figure: Comment box

Figure: Preparation box

Figure: Separate box

Q. Make a flowchart to input temperature, if temperature is less than 32 then print "below freezing" otherwise print "above freezing"?

Ans.

Figure: Flowchart example of C program

Sample C Program

/*Program to add three numbers and calculate them average*/

#include<stdio.h>

#include<conio.h>

void main()

{
//first we declare of variable

int n1=10, n2=20, n3=30;

int sum, avg;

clrscr();

sum=n1+n2+n3;

avg=sum/3;

printf("\nSum Of Threes numbers is %d",sum);

printf("\nAverage of n1,n2,n3=%d",avg);

}

Output of the above program :

Sum of Threes numbers is 60

Average of n1, n2, n3=20

Let's discuss some useful tips of above program:

In C language there are two types of comments written as :

1. Single line comment:single line comment give by two forward slash (//).Example : // this is single line comment

2. Multi line comment: Multi line comment give by this form : /* it is a multi line comment and its can be spilt into several lines.*/

Comments can't be nested.
main() is a function and gives to a set of statement. If a function is void then it is nothing return otherwise its always return value.
Any variable used in the program must be declared before using it.
printf() function: It is used to print the value at console. The syntax of printf() as following: printf("<format string>",<variable name>);

format string can be following type:

%d=printing integer values

%f=printing real values

%c=printing character values

"\n" is one of the several escape sequence in C.It is force to cursour go to next line.

What is Data Type in C?

In the C Programming Language, Data Types refers to an extensive system for declaring variable of different types.
A data types tells the following things about the related variable:

What is the size of the variable?
How much its occupies space in storage?
How the variable bit mapped for its operation?

All data types used in C programming, generally defined in standard library header files. In header files, all the characteristic such as size, space etc. of data-types has been defined.

If you want, you can create your own custom data types in C.

There are mostly following Data Types in C as:

1. char Data Type

2. int Data Type

3. long Data Type

4. double Data Type

5. float Data Type

6. Long Double Data Type

7. function Data Type

8. pointer Data Type

9. array Data Type

10. enum Data Type

11. struct Data Type

12. typedef Data Type

 16 bit V/S 32 bit compiler meaning in C

 Characters data type - signed char V/S unsigned char

 Integers data types

signed int V/S unsigned int
short int V/S long int

 float VS double data type

 long double data type

 Comparison of all data types

C Operators

What is operators?

In simple word operators are those which operator anything like as data, maths, information etc i.e.. When we talking about C operators, i want to say you that C is very rich in operators. Operators tells to compiler that what do with data. There are mainly operators in c as following:

1. Logical Operators

2. Bitwise Operators

3. Relational Operators

4. Assignment Operators

5. Sizeof Operators

6. Increment and Decrement operators

7. Comma operators

8. Type cast operator

9. Conditional operators or ternary operators

Sometime operators are divided according numbers of operands. So there are three types of operators as following :

Operators
	Unary	Binary	Ternary
operand	Single	double	third
works	right to left	left to right	left to right
Example_1	++ , --	+, -, *, /	? :
Example_2	! , ~	&& , \|\|

All of these above operators we discuss step by step in next chapters.

Logical Operator

When we use if, for, while then use one condition at once time what happen if we examine condition more than one? In this case we use logical operators. So logical operators are used to combine two or more condition.
There are three types of logical operators as following:

Operator symbol	Name
&&	Logical AND
\|\|	Logical OR
!	Logical NOT

LOGICAL AND OPERATOR ( &&)

The condition is true if and only if both two expression are true otherwise condition false. The truth table of logical AND operators end of this chapter.

LOGICAL OR OPERATOR ( || )

The condition is true if one of expression is true and condition will be false only if both expression are false. See example of || operator at end of this chapter.

LOGICAL NOT OPERATOR ( ! )

It reverse the expression i.e if the expression evaluates to a non-zero value, then applying! operator to it results into a 0 and vice versa. The final result (after applying!) 0 or 1 is considered to be false or true respectively.

Example of above three operators:

//following table con = condition.

con 1	Con 2	con 1 && con 2	con 1 \|\| con 2	! con 1	! con 2
False	False	False	False	True	True
False	True	False	True	True	False
True	False	False	True	False	True
True	True	True	True	False	False

Some numerical example :

if(10>5 && 1000<2001) // True

while( ; num>=1 || num<=100 ; ) // if num=1 True

Now some discuss of NOT operator when we write condition if( 1 ! = 0 ) what is mean it? It is mean "one is not equal to zero", so is condition TRUE or False? It is true.

Let's understand following example :

if(sex!='M')

printf("Person is Female");

else

printf("Person is Male");

In above example evaluate first printf if condition is false otherwise evaluate second printf.

!(x<22) it is also we write (x>=22) // both are equal.

Bitwise operators

The smallest element in memory on which are able to operate is called byte; and the programming language are byte oriented. One of the c powerful features is a set of bit manipulation operators. There are various bitwise operators in C as following table; we learn all step by step :

Operators	Name
&	Bitwise AND
\|	Bitwise OR
^	Bitwise XOR(exclusive OR)
>>	Left shift
<<	right shift
~	One's complement

These operators can operate upon ints and chars but not on floats and doubles. Bits are numbered from zero onwards, increasing from right to left as following figure:

8 bit Character

16 bit Integer

Bitwise AND Operator (&)

The & operator operates on a pair of bits to yield a resultant bit. The rules that decide the value of the resultant bit also called truth table are shown below:

Bit x	Bit y	x & y
0	0	0
0	1	0
1	0	0
1	1	1

The best use of the AND operator is to check whether a particular bit of an operand is ON or OFF. The meaning of ON means 1 and OFF means 0. The following program puts this logic clear:

/*Example of bitwise AND operator*/

#include<stdio.h>

#include<conio.h>

Void main ()

{

int x=45;

int y=37;

int z;

clrscr();

z = x & y;

printf("\nValue of z=%d",z);

}

Output of above program:

Value of z=37

In above program compiler first calculate the binary x and y which is 111101 and 100101 respectly. After this its work on bitwise operator and final result is 37 which binary code are 100101. The following table shown the result :

Values	binary code
x = 45	111101
y = 37	100101
z = x & y	100101

Bitwise OR ( | )

Truth table for bitwise OR are as following:

x	Y	z = x \| y
0	0	0
0	1	1
1	0	1
1	1	1

Bitwise XOR ( ^ )

It is also called exclusive OR. If there are similar bit then its return 0 otherwise its return 1. Let watch truth table of x^y :

x	Y	z = x ^ y
0	0	0
0	1	1
1	0	1
1	1	0

Example of exclusive OR :

x = 75

y = 64

z = x ^ y

x = 1 0 0 1 0 1 1

y = 1 0 0 0 0 0 0

z = 0 0 0 1 0 1 1

hence, the value of z=11

Bitwise right shift ( >> )

Right shift operator shifts each bit in its left operand to the right. The number of places the bits are shifted depends on the number following the operator i.e. its right operand.

In simple meaning of bitwise right shift as:

Insertion (zero) > deletation

Example of right shift operator:

x = 15

y = x >> 2

[x=15 before right shifting ] 0000 0000 0000 1111

[y = x >> 2 during right shifting] 000000 0000 0000 1111

[y = x >> 2 after right shifting] 0000 0000 0000 0011

so now value of y=3.

Left Shift operator ( << )

This is similar to the right shift operator, the only difference being that the bits are shifted to the left, and for each shifted, a 0 is added to the right of the number. Following structure shows it:

deletation > insertion (zero)

Example of right shift operator:

x = 15

y = x << 2

[x=15 before right shifting ] 0000 0000 0000 1111

[y = x << 2 during right shifting] 0000 0000 0000 111100

[y = x << 2 after right shifting] 0000 0000 0011 1100

so now value of y=60.

One's complement ( ~ ) or Tilde

It is reverse the bit i.e. if bit is 0 then its return 1 and when bit is 1 it is return 0.

example of tilde:

x = 15

y = ~ x

(15)₁₀ = 0000 0000 0000 1111

y = ~ x 1111 1111 1111 0000

hense, 65535 - 15 = 65520.

so the value of y is 65520.

Arithmetic Operator

Arithmetic operators are special mathematical symbol which do all arithmetical calculation of the programs. Following table display the operators and their works:

Name of operators	Symbol	works	example
Addition operator	+	Add the numbers	sum=7+8+1=16
Subtract operator	-	Subtraction of numbers	sub=100-50=50
Multiply operator	*	Multiple of numbers	muti=8*9=72
Modulus operator	%	Find the reminder of numbers	mod=45%40=5
Division operator	/	Find the division of numbers	div=45/40=1

Relational Operator

When we write program, many time we requirement to comparison of two or more data, in that case we uses relational operators. There are following relational operators as following :

Operators Name

> Greater than

< Less than

= Equals to

>= Greater than equals to
<= Less than equals to

!= Not equals to

The syntax of relational expression as :

<data value 1>Relational operator<data value 2>

Example :

10 >= 5

-50 <= 1

0 != 0

Sizeof operator

Sizeof operator calculate the size of data i.e. how many bit a specific data having.

Syntax of sizeof operator:

Printf ("<format string>",sizeof<(data type variable)>);

/*Program to sizeof operator*/

#include<stdio.h>

#include<conio.h>

void main()

{

int x=10;

clrscr();

printf("\nSize of x is %d",sizeof(x));

getch();

}

Output of above program:

Size of x is 2

We read in data type chapter that an int allocate only 2 byte in memory, Hence, x = 2.

Increment and Decrement operators

Increment operators (++)

Increment operators are increase the value of subsequent. value may be increase according to the programmer.
Increment operator are two types as follows :

1. Post increment

2. Pre increment

Decrement operators ( -- )

decrement operators decrease the value to one, two and so on.
As like Increment operators, decrement operators are also two type as :

1. Post decrement

2. Pre decrement

Before we more discuss about increment and decrement operator, let understand some expression; that's are using in all operators.

Now some issues of pre and post increment and decrement, we will discuss after solve following programming :

x = 5       x = 5    x = 5
x = x+1     ++x x++
x = 6     x = 6      x=5

In above program u notice that value of x increase to one in all three expression but after the increasing one, the final value of x in not same, third box result is differ to another two boxes. Now you know that c operators are mostly three types, ++ and -- operators are Unary operators.

Post increment or decrement are lowest precedence so it is solve at the

End of program. Hence above program in third box first value of x is print i.e. 5 after, it is increase.

Unary operators are solve right to left.

Q.1 Solve the expression in C language compiler ,assuming x,z are integer variables:

z = x++ + x++

where x=7

Ans.

stepwise evaluation of this expression is shown below :

z = x++ + x++ + ++x

//post increment of x=2

z = x + x + ++x

//++x increase the value of x one so x=8

/*Now all pre and post increment/decrement are solved so we write the the expression in normal mathematical expression*/

z = x + x + x

//put the current value of x i.e. 8

z = 8 + 8 + 8

z = 24

syntax : x=current value-post increment/decrement

so x = 8 + 2

x = 10

Q.2 Solve the following expression :

z = ++x + y-- - ++y - x-- - x-- - ++y - x--

where x = 7

y = -3

Ans.

z=++x + y-- - ++y - x-- - x-- - ++y - x—

/* post decrement of x=3 and

post decrement of y=1 */

z= ++x + y - ++y - x - x - ++y - x

/* its unary operator so we solve it from

right to left*/

z=++x + y - ++y - x - x - y - x

//now y=-3+1=-2

z=++x + y - y - x - x - y - x

//now y=-2+1=-1

z=x + y - y - x - x - y - x

//now x=7+1=8

/*now all increment and decrement operators

all solved so we put the current value of x

and y.*/

z= 8 + (-1) - (-1) -8 - 8 - (-1) - 8

z= 8 - 1 + 1 - 8 - 8 + 1 - 8

z= - 16 + 1

z= -15

x=8-3=5

y=-1-1=-2

Related some increment or decrement operators exercise:

Q.3 solve the following equations:

z = x++ + ++y - x-- + --y

where x = 7 and
y = 9

hint:(For your cross-checking, answer is x=7, y=9 and z=18).

Q.4 solve the following equations:

z = x++ * y++ / ++x - --y % x++

where x = 5 and
y = 2
hint:(For your cross-checking, answer is x=8, y=2 and z=0).
--------------------------------------------------------------------------------
Q.3 answer with explanation :

z = x++ + ++y - x-- + --y
where x = 7 and
y = 9

Ans:

post decrement of x = 1
post increment of x = 1

z = x + ++y - x + --y
z = x + ++y - x + y // now y = 9-1 = 8
z = x + y - x + y // now y = 8+1 = 9
// now put the value of x and y
z = 7 + 9 - 7 + 9
z = 9 + 9
z = 18

Hence, our final answer will be:

x = 7 - 1 + 1 = 7
y = 9
z = 18

Comma operator

Comma operator ( , )

Evaluate of comma operator- Left to right.
Uses of comma operator as following :

1. Multiples declaration

2. Multiples initialization

3. Multiples variation

4. Multiples statement

Example of comma operator

1. int x=0,y=1,z=2;

2. for(x=0 , y=1, z=2 ; condition1 , condition2 ;increment/decrement)

Type-cast operator

The type cast operator is very important in C. Cast operator uses in convert one data type to another data types. Type casting may be two types:

1. Implicit type cast

2. Explicit type cast

Implicit type cast

In C, implicit type cast are automatically handled by compiler i.e. when two or more data types are getting execution then the final data-type will be that data type as it is declared, i.e it is not depend on conversion of data type.

It is clear understand by example as:

#include<stdio.h>

#include<conio.h>

void main()

{

int i,j;

float f;

double d;

i=d*f+f*j;

}

what you think, what will be data type of i?

it is double!! No, right answer is int. You see in program that double has high priority or precedence of float and int, so result of data type will be comes in double but when result is assign in i, it will be convert in int because i is declared as int. It is implicit type casting.

Explicit type cast

An explicit type cast is a cast that we should specify invoke with either the cast. The compiler does not automatically invoke to resolve the data type conversion.

Let's understand explicit with example:

/*A student marks of three subject as m1,m2,m3 and calculate percentage(per)*/

#include<stdio.h>

#include<conio.h>

void main()

{

int m1=70,m2=70,m3=100,total;

float per;

total=m1+m2+m3;

per=total/300*100;

printf("%f",per);

}

output:- 0.000000

Surprise, let's explain to me, it is a common type cast mistake, look at per=total/300*100; statement. In this statement first of all total/300 will be solve so total(240) and 300 are int hence 240/300 will be produce a float value so result is 0.000000. These mistake may me solved by three ways as:

1. We mention type cast in above program as:
/*demonstration of type casting*/

#include<stdio.h>

#include<conio.h>

void main()

{

int m1=70,m2=70,m3=100,total;

float per;

total=m1+m2+m3;

per=(float)total/300*100;

printf("%f",per);

}

output:- 80.000000

2. We used total as float variable.

#include<stdio.h>

#include<conio.h>

void main()

{

int m1=70,m2=70,m3=100;

float per,total;

total=m1+m2+m3;

per=total/300*100;

printf("%f",per);

}

output:- 80.000000

3. we convert int to float to the 300 by adding decimal portion.
#include<stdio.h>

#include<conio.h>

void main()

{

int m1=70,m2=70,m3=100,total;

float per;

total=m1+m2+m3;

per=total/300.0*100;

printf("%f",per);

}

output:- 80.000000

Ternary operator

Main features of ternary operators as follows :

There are three operand.
It works from left to right
Example of ternary operator is conditional operator. Symbol of conditional operator : condition ? True_parts : False_parts

Intro if-else

In C language there are three major decision making instruction as if statement, the if-else statement, and the switch statement. And one also minor decision making instruction is conditional operator.

The keyword if tells the compiler that what follows is a decision control instruction. The condition following the keyword if is always enclosed within a pair of parentheses. If the condition, whatever it is, is true, then the statement is executed, and If the condition is not true, then statement is not executed.

Let's demonstrates the use of if-else with c program:
/*demonstrates of if-else statement*/
#include<stdio.h>
#include<conio.h>
void main()
{
int n=10;
if(n>=15)
printf("n is greater!!");
else
printf("n is less than!!");
getch();
}
Output :
n is less than!!
On execution of this program, when compiler check condition 10>=15, the condition is false so its execute else part statement i.e. n is less than!!.
Now try to write below program for more familiar with if-else:

Q. Write a C program to read quantity and price for each item. Calculate the total expenses, and if the quantity is more than 1000 than giving discount is 20%.

Ans.

/*Calculate the total expenses*/

#include<stdio.h>

#include<conio.h>

void main()

{

int quant,dis=0;

float tot,rate;
clrscr();

printf("Enter quantity : ");

scanf("%d",&quant);

printf ("\nEnter rate: ");

scanf("%f",&rate);

if(quant>1000)

dis=20;

tot=(quant*rate)-(quent*rate*dis/100);

Printf("\nTotal expenses = %f", tot);

getch();

}

Output :

Enter quantity :750

Enter rate : 35.54

Total expenses = 25905.000000

Enter quantity: 1450

Enter rate : 9.50

Total expenses = 12397.500000

Forms of if-else

There are many way to write if-else statement in program, it can be single if statement, both if-else statement, If-else if statement and etc. There are no limit on how deeply the if's and the else's can be nested. Now let's start to form of if-else:

1. if (condition)

do this;

2. if (condition) {

do this;

and this;

}

3. if(condition)

do this;

else

do this;

4. if(condition)

{

do this;

and this;

}

else

do this;

5. if(condition)

{

do this;

and this;

}

else

{

do this;

and this;

}

6. if(condition)

do this;

else

{

if(condition)

       do this;
     else
     {
       do this;
       and this;
     }
   }
7. if(condition)
{
      if(condition)
       do this;
     else
     {
       do this;
       and this;
     }
   }
   else
     do this;
8. if(condition)
      do this;
    else if(condition)
      do this;
    else if(condition)
      do this;
    else
      do this;

And now you thinking, what the hell condition? Don't worry, it’s quite simple and easy to use in programming. In condition part we put data, numeric values with with appropriate operator like as Logical operator, Arithmetic operator etc.

More if-else

Notice the following if statement :

if(expression)

statement;

Here the expression can any valid expression including a relational expression. We can even use arithmetic expression in the if statement. For example all the following if statement are valid :

if(10 + 5 % 7)

statement;

if(n=20)

statement;

if(-15)

statement;

if(-2.0)

statement;

In C every expression is evaluated in terms of zero and non-zero values.
Note: that in C a non-zero value is considered to be true, whereas a 0 is considered to be false.

The default scope of the if statement is only the next statement. So, to execute more than one statement they must be written in a pair of braces

If else statement and flowchart

Decision Control Statements and Flowchart

The if Statement
It is used to execute an instruction or sequence/block of instruction only if a condition is fulfilled.
Difference forms of implements if-statement are:

Simple if statement
if-else statement
Nested if-else statement
else if statement

Figure: Simple if statement syntax and flowchart

Figure: if-else statement syntax and flowchart

Nested if-else statement

In nested if...else statement, an entire if...else construct is written within either the body of the if statement or the body of an else statement.

The syntax is as follows:

if(condition_1)

{

if(condition_2)

{

block statement_1;

}

else

{

block statement_2;

}

else

{

block statement_3;

}

block statement_4;

Figure: nested if-else statement flowchart

Else if statement

It is used in multi-way decision on several conditions. This works by cascading comparisons. As soon as one of the conditions is true, the statement or block of statements following them is executed and no further comparison are performed.

The else...if syntax is as follows:

if(condition_1)

block statement_1;

else if(condition_2)

block statement_2;

else if(condition_n)

block statement_n;

else

default statement;

Figure: flowchart for else...if statement

Looping concept

The program that we have developed so far used either a sequential or a decision control instruction.

The versatility of the computer lies in its ability to perform a set of instructions repeatedly. This involves repeating some portion of the program either a specified number of times or until a particular condition is being satisfied. This repetitive operation is done through a loop control instruction.

Loops can be created to executed a block of code for a fixed number of times. Alternatively, loops can be created to repetitively execute a block of code until a Boolean condition changes state.
For instance, the loop may continue until a condition changes from false to true, or from true to false. In this case, the block o code being executed must update the condition being tested in order for the loop to terminate at some point. If the test condition is not modified somehow within the loop, the loop will never terminate. This created a programming bug known as an infinite loop.

There are three method by way to which we can repeat a part of a program. They are:

1. Using a for statement

2. using a while statement

3. Using a do-while statement

for Loop

At this point you think, there is already while loop function then what we need one more loop function? The answer is that for is easy to use and allows us to specify three things in single line, these three things are:

1. Setting a loop counter to an initial value

2. Testing the loop counter to determine whether its value has reached the number of repetitions desired.

3. Increasing or Decreasing the value of loop counter.

The general form of for statement is as under:

for (initialize counter; test counter; increment/decrement counter)

{

do this;

and this;

and that;

}

It is important to note that the initialization ,testing and incrementation part of a for loop can be replaced by any valid expression, thus the following for loops are valid:

for(i=5; i; i--)

printf("%d",i);

for(i<=5; j=10; j=0)

printf("%d",i);

for(i=1; i<=10; printf("%d",i++))

;

for(scanf("%d",&i); i<=5; i++)

printf("%d",i);

Demonstration of for loop

/*demonstration for loop program*/

/*program to print cprogrammingcodes in five times*/

#include<stdio.h>

#include<conio.h>

void main()

{

int i;

clrscr();

for(i=1; i<=5; i++)

{

printf("cprogrammingcodes");

printf("\n");

}

getch();

}

Output of above program:

cprogrammingcodes

Versions of for loops

Now we learn how many different types for uses to print one to ten numbers.

(a) #include<stdio.h>

#include<conio.h>

void main()

{

int i;

clrscr();

for(i=1; i<=10; i++)

printf("%d\n",i);

}

(b) #include<stdio.h>

#include<conio.h>

void main()

{

int i;

clrscr();

for(i=1; i<=10;)

printf("%d\n",i);

i++;

}

#include<conio.h>

void main()

{

int i;

clrscr();

i=1;

for(; i<=10; i++)

printf("%d\n",i);

}

(d) #include<stdio.h>

#include<conio.h>

void main()

{

int i;

clrscr();

i=1;

for(; i<=10 ;)

printf("%d\n",i);

i++;

}

(e) #include<stdio.h>

#include<conio.h>

void main()

{

int i;

clrscr();

for(i=1; i++<=10;)

printf("%d\n",i);

}

(f) #include<stdio.h>

#include<conio.h>

void main()

{

int i;

clrscr();

for(i=0; ++i<=10;)

printf("%d\n",i);

}

(g) #include<stdio.h>

#include<conio.h>

void main()

{

int i;

clrscr();

i=1

for(; i++<=10;)

printf("%d\n",i);

}

Multiple Initializations and increment/decrement in the for loop

The initialization expression of the for loop can contain more than one statement by a comma. For example:

for(i=0, j=10; i<=j ; i++,j--)

Thus we see, that multiple statement can uses to initialization and increment (or decrement). But notice there must be only one statement allowed in the test expression. This expression may contain several condition linked using logical operators as:

for(i=0, j=10; i<=j || i==j ; i++,j--)

Nesting of for Loops

The way if statement can be nested, similarly whiles and fors can also be nested. Let's understand the nesting of for loops through program:

/*demonstration of nested for loop*/

#include<stdio.h>

#include<conio.h>

void main()

{

int r,c,s;

clrscr();

for(r=1; r<=2; r++)/*outer loop*/

{
for(c=1; c<=2; c++) /*inner loop*/
{
s=r+c;
printf("r=%d c=%d sum=%d\n",r,c,s);
}
}
getch();
}

output of above program

r=1 c=1 sum=2

r=1 c=2 sum=3

r=2 c=1 sum=3

r=2 c=2 sum=4

Thus we see in above program that, the body of outer loop is indented, and the body of the inner for loop is further indented. These multiple indentations make the program easier to understand.

while loop

It is often the case in programming that we want to do something a fixed number of times. Perhaps we want to calculate gross salaries, or convert temperatures form centigrade to Fahrenheit for 20 different cities. The while loop is ideally suited f or such cases.

Syntax of using while loop:

initialise loop counter

while(valid condition)

{

statement1;

statement2;

statement3;

statement4;

increment or decrement loop counter;

}

some basic rule of while loop:

The statements within the while loop would keep in getting executed till the condition being tested remains true. When the condition becomes false, the control passes to the first statement that follows the body of the while loop.

The condition being tested may use relational or logical operators as shown in the following examples:
while(x<=20)
while(x>=20 && x<=50)
while(x>=10 || (i>=10 && i<=20)||y==15)
Almost always, the while must test a condition that will eventually become false, otherwise the loop would be executed forever, indefinitely.
It is not necessary that a loop counter must only be an int. It can even be a float.
Example of while loop:

#include<stdio.h>

#include<conio.h>

void main()

{

int i=1;

while(i<=5)

{

printf("%d\n",i);

i=i+1; //i++;

}

getch();

}

Output of above program:

Nested while loop

One or more loop which require execute again and again then these loop and loops place in separate block is known as nested loop.
Example of nested while loop:

/*demonstration of nested while loop*/

#include<stdio.h>

#include<conio.h>

void main()

{

int r,c,s;
clrscr();
r=1;

while(r<=5) /*outer loop*/

{
c=1;
while(c<=2) /*inner loop*/
{
   s=r+c;
   printf("r=%d c=%d sum=%d\n",r,c,s);
   c++;
}
printf("\n");
r++;
}
getch();
}

Output of above program:

r=1 c=1 sum=2

r=1 c=2 sum=3

r=2 c=1 sum=3

r=2 c=2 sum=4

r=3 c=1 sum=4

r=3 c=2 sum=5

r=4 c=1 sum=5

r=4 c=2 sum=6

r=5 c=1 sum=6

r=5 c=2 sum=7

do-while loop

Now we know about for, while loop that executed the statement within them finite number of times. However, in real life programming, one comes across a situation when it is not known beforehand how many times the statement in the loop are to be executed. In this situation we used do-while loop.

do-while tests the condition after having executed the statement within the loop i.e. do-while would executed its statement at least once, even if the condition fails for the first time. For example notice in following program:

/*demonstration of do-while*/

#include<stdio.h>

#include<conio.h>

void main()

{

clrscr();

{

printf("Its work!!");

}while(10<1);

getch();

}

Output of above program:

Its work!!

In above program, the printf() would be executed once, since first the body of loop is executed and then the condition tested, 10<1 condition false so loop terminate and go to next statement.

/*program to find factorial value of any number, and it is execute unknown number of times when user enter no, then program should be terminate.*/

#include<stdio.h>

#include<conio.h>

void main()

{

int n,f=1;

char choice;

clrscr();

{

printf("Enter number : ");

scanf("%d",&n);

while(n>=1)

{

f=f*n;

n--;

}

printf("Factroial value of %d is %d",n,f);

printf("\nCalculate another value y/n :");

scanf("%c",&choice);

}while(choice=='y');

}

output of above program:

Enter number :5

Factorial value of 5 is 120

Calculate another value y/n :y

Enter number :4

Factorial value of 4 is24

Calculate another value y/n :n

In above program, the do-while loop would keep getting executed till the user continues to answer y. When user enter answer n,the loop terminate, since the condition fails.

Odd Loop

What is odd loop?
In real life programming, there are many times comes a situation when we don't know how many times the statements in the loop are to be executed.
There is comes concept of odd loop.
Execution of loop an unknown number of times can be done by - while, for and do...while loops.

/*A demonstration of odd loop using do...while*/
#include<stdio.h>
int main()
{
int n;
char answer;
do
{
printf("Enter any number : ");
scanf("%d", &n);
printf("Square of %d is %d",n,n*n);
fflush(stdin);
printf("\nWant to calculate more square y/n: ");
scanf("%c", &answer);
}while(answer=='y');
return 0;
}

The output of above program would be:

Figure: Screen shot of odd loop (do...while) to calculate
square of number C program

The above odd loop program we can write using for loop as:

/*odd loop using for loop of calculate square number C program*/

#include<stdio.h>
int main()
{
int n;
char ans='y';
for(; ans=='y' ; )
{
printf("Enter any number : ");
scanf("%d", &n);
printf("Square of %d is %d",n,n*n);
fflush(stdin);
printf("\nWant to calculate more square y/n: ");
scanf("%c", &ans);
}
return 0;
}

The output of above program would be:

Figure: Screen shot of odd loop (for) to calculate
square of number C program

The odd loop program we can write using while loop as:
/*odd loop using while loop of calculate square number C program*/
#include<stdio.h>
int main()
{
int n;
char ans='y';
while(ans=='y')
{
printf("Enter any number : ");
scanf("%d", &n);
printf("Square of %d is %d",n,n*n);
fflush(stdin);
printf("\nWant to calculate more square y/n: ");
scanf("%c", &ans);
}
return 0;
}

The output of above program would be:

Figure: Screen shot of odd loop ( while ) to calculate
square of number C program

break statement

When we writing programming code, we often come across situations where we want to jump out of a loop instantly, without waiting to get back to the conditional test. The keyword break allows us to do this. When break is encountered inside any loop, control automatically passes to the first statement after the loop. A break is usually associated with an if.
The keyword break, breaks the control only from the while in which it is placed.
Let's understand break with c program example:

/*demonstration of break statement through c program*/

#include<stdio.h>
#include<conio.h>
void main()
{
int i=5;
clrscr();
while(i>=1)
{
if(i==2)
{
printf("\nIt is equal to two!!");
break;
}
printf("%d\n",i);
i--;
}
getch();
}

Output:
5
4
3
It is equal to two!!

Thus, it is clear that a break statement takes the execution control out of the loop.
In above program, if we omitted break statement then what will be output? The answer is
5
4
3
It is equal to two!!
2
1

because when i's value is 2, condition will be satisfy and executed printf statement, after that compiler goes to next statement i.e. printf("%d",i); because loop do not terminate and it is run till the i value is not less than 1.

search prime number

Q. Write a C program to find whether a number is prime or not.

Definition of prime number: A prime number is one,which is divisible only by one or itself. And it’s must greater than 1.

And if number is not prime, it is called composite number and vice versa.

Ans.

#include<stdio.h>

int main()

{

int x,num;

printf("Enter number : ");

scanf("%d",&num);

x=2;

while(x<=num-1)

{

if(num%x==0)

{

printf("Number is not prime!!");

break;

}

x++;

}

if(x==num)

printf("Number is prime!!");
getch();

return 0;

}

output of above program :Enter number : 7Number is prime!!

continue statement

when we write program, if we want to take control to the beginning of the loop, bypassing the statements inside the loop, which have not yet been executed, in this situation we uses continue. continue is c reserved keyword in C. When continue is encountered inside any loop, control automatically passes to the beginning to the loop.
A continue is usually associated with an if.
Let's understand continue with example:

/*demonstration of continue statement*/
#include<stdio.h>
#include<conio.h>
int main()
{
int i,j;
for(i=1; i<=2; i++)
{
   for(j=1; j<=2; j++)
   {
    if(i==j)
   continue;
    printf("\n%d %d",i,j);
   }
}
getch();
return 0;
}

Output:

1 2
2 1

Explanation: When the value of i equals that of j, the continue statement takes the control to the for loop(inner) bypassing the rest of the statements execution in the for loop(inner).

Let's understand continue statement with another example:

/*demonstration of continue statement*/

#include<stdio.h>
#include<conio.h>
int main()
{
int i;
for(i=1; i<=10; i++)
{
   if(i==6)
     continue;
   printf("%d ",i);
}
printf("\nNow we are out of for loop");
getch();
return 0;
}

Output:-

1 2 3 4 5 7 8 9 10

Now we are out of for loop

Explanation: As when the value of i will becomes 6 it will move for the next iteration by skipping the iteration i=6.

switch-case statement

In some programming situation, when there are number of choices and we want to choose only appropriate choice, in that situation C provided switch statement. Thus switch statement allows us to make a decision from the number of choices.

The switch statement also known as switch-case-default.
Since, the switch statement known for decision maker.
Syntax of switch statement:
switch(integer expression)
{
case 1 :
   do this;
   break;
case 2 :
   do this;
   break;
case 3 :
   do this;
   break;
case 4 :
   do this;
   break;
default :
   and this;
   break;
}

Example of switch-case-default statement:

#include<stdio.h>
#include<conio.h>
int main()
{
int r=4;
  switch(r)
{
   case 1 :
   printf("\nI am in case 1");
   break;
   case 2 :
   printf("\nI am in case 2");
   break;
   case 3 :
   printf("\nI am in case 3");
   break;
   case 4 :
   printf("\nI am in case 4");
   break;
   case 5 :
   printf("\nI am in case 5");
   break;
   default :
   printf("\nI am in default");
   break;
}
getch();
return 0;
}

Output: I am in case 4

Different types of switch statement

(a) In switch statement case arrangement may be ascending order, descending order, scrambled order. So the following program should be valid and run:

#include<stdio.h>

#include<conio.h>

int main()

{

int r=44;

switch(r)

{

case 210 :

printf("\nI am in case 210");

break;

case 10 :

printf("\nI am in case 10");

break;

case 1 :

printf("\nI am in case 1");

break;

case 44 :

printf("\nI am in case 44");

break;

default :

printf("\nI am in defalut");

break;

}

getch();

return 0;

}

Output: I am in case 44

(b) C also allowed to use char values in case and switch statement as:

#include<stdio.h>

#include<conio.h>

int main()

{

char a='n';

switch(a)

{

case 'm' :

printf("\nI am in case m");

case 'n' :

printf("\nI am in case n");

case 'o' :

printf("\nI am in case o");

case 'p' :

printf("\nI am in case p");

default :

printf("\nI am in default");

}

getch();

return 0;

}

Output: I am in case n

Note: When above program run, 'm', 'n', 'o', 'p' are actually replaced by subsequent ASCII(American Standard Code for Information Interchange) code.

switch(r+c*i)

switch(10+20%2*r)

switch(r+10*c)

switch(r>10 || c<20)

Above all switch statement are valid.

And expression can also be used in cases provided they are constant expression.

Thus case 10+15 is correct,

and however case r+c is incorrect.

(d) The switch statement is very useful while writing menu driven program.

(e) The break statement when used in a switch takes the control outside the switch. However, use of continue will not take the control to the beginning of switch.

(f) The case keyword is followed by an integer or a character constant.

goto statement

The goto statement is used to alter the normal sequence of program instructions by transferring the control to some other portion of the program.

The syntax is as follows:

goto label;

Here, label is an identifier that is used to label the statement to which control will be transferred. The targeted statement must be preceded by the unique label followed by colon.

label: statement;

It is recommended that as possible as skip the goto statement because when we use goto then we can never be sure how we got to a certain point in our code. They obscure the flow of control.

Note:- goto can never be used to jump into the loop from outside and it should be preferably used for forward jump.

Let us consider a program to illustrate goto and label statement:

/*program to demonstration of goto statement*/

#include<stdio.h>

#include<conio.h>

void main()

{

int n;

clrscr();

printf("Enter one digit number: ");

scanf("%d",&n);

if(n<=6)

goto mylabel;

else

{

printf("Now control in main funcion.");

exit();

}

mylabel:

printf("Now control in mylabel.");

}

Output:-

Enter one digit number:9

Now control in main function.

Enter one digit number:4

Now control in mylabel.

Flowchart for switch-case

How to write switch case flowchart?

switch case statement:

switch( choice )
{
case 1:
statement 1;
break;

case 2:
statement 2;
break;

case 3:
statement 3;
break;

case n:
statement n;
}

(in above module n = number of cases.)

switch case flowchart:

Figure: flowchart of switch case statement in C

Storage classes

Every variable in C or other language have two main features namely:

1. Data Types

2. Storage class

From C compiler's point of view, a variable name identifies some physical location within the computer where the string of bits representing the variable's value stored. There are basically two kinds of locations in a computer where such a value may be kept- Memory and CPU registers. It is the variable's storage class that determines in which of there two types of locations, the value is stored.

Moreover, a variable's storage class tells us:

1. Memory location i.e. where variable would be stored.

2. Initial value or default value of variable

3. What is scope of the variable

4. What is life of the variable

Scope of variable:

Scope of variable i.e. in which function the value of the variable would be available.

Life of the variable:

The life of the variable i.e. how long would the variable exists.

There are four storage classes in C :

1. Automatic storage class

2. Register storage class

3. Static storage class

4. External storage class

5. Comparison of storage classes

Automatic Storage Class

Automatic storage class is default storage class i.e. if there are nothing to add storage class in variable then by default it would be automatic storage class.
The features of a variable defined to have an automatic storage class are as under:

Storage	Memory
Keyword	auto
Default initial value	Garbage value i.e. an unpredictable value
Scope	Local to the block, in which the variable is defined
Life	Till the control remains within the block in which the variable is defined

Scope and life of an automatic variable is illustrated in the following program:

/*program to shows the life and scope of automatic variable*/
#include<stdio.h>
int main()
{
auto int i=1;
{
auto int i=2;
{
auto int i=3;
printf("\n%d",i);
}
printf("\n%d",i);
}
printf("\n%d",i);
return 0;
}

OUTPUT:-

3
2
1

In above program, compiler treats the three i's as totally different variables, since they are defined in different block. Once the control comes out of the innermost block, the variable i with value 3 is lost, and hence the i in the second printf() refers to i with value 2. Similarly, when the control comes out of the next innermost block, the third printf() refers to the i with value 1. Hence it is clear that scope of of i is local to the block in which it is defined.

Following program shows how an automatic storage class variable is declared, and what happen if variable is not initialise i.e. garbage value.

#include<stdio.h>
int main()
{
auto int i,j;
printf("\ni=%d \nj=%d",i,j);
return 0;
}

OUTPUT:-

i=54
j=3564

Where, 54 and 3564 are garbage values of i and j. When you run this program, you may get different values, since garbage values are unpredictable.

Register Storage Class

A value stored in a CPU register can always be accessed faster than the one that is stored in memory. Therefore, if a variable is used at many places in a program, it is better to declare its storage class as register.
The features of a register storage variable as following manner:

Storage	CPU registers
Keyword	register
Default initial value	Garbage value i.e. an unpredictable value
Scope	Local to the block, in which the variable is defined
Life	Till the control remains within the block in which the variable is defined

There are no guaranty that we have declare any variable as register and it would be stored in CPU register! Why? The reason is because CPU register are limited, and they may be busy doing some other task. In this case that variable works as default storage class i.e. automatic storage class.
Note: Any variable stored in CPU register or not depend on capacity of microprocessor. For example, if the microprocessor has 16-bit register then they cannot hold a float value or a double value, which require 4 and 8 bytes respectively.
However, if you use the register storage class for float, double variable then you won't get any error messages because compiler treat it as default storage class i.e. auto storage class.

All looping program where a variable are frequently used, declare variable as register.

/*shows uses of register storage class*/
#include<stdio.h>
int main()
{
register int i;
for(i=10; i>=0; i=i-2)
printf("%d ",i);
return 0;
}

OUTPUT:-

10 8 6 4 2 0

Static Storage Class

The features of static storage class are as following:

Storage	Memory
Keyword	static
Default initial value	Zero
Scope	Local to the block, in which the variable is defined
Life	Value of the variable persists between different function calls.

Let's compare static class with auto storage class for better understanding:

/*auto class*/

#include<stdio.h>
void add();
int main()
{
add();
add();
add();
add();
return 0;
}
void add()
{
auto int i=1;
printf("\n%d",i);
i=i+1;
}
OUTPUT:-
1
1
1
1

/*static class*/
#include<stdio.h>
void add();
int main()
{
add();
add();
add();
add();
return 0;
}
void add()
{
static int i=1;
printf("\n%d",i);
i=i+1;
}

OUTPUT:-
1
2
3
4

The above both program consist of two functions main() and add(). The function add() gets called from main() four times. Each time it prints the value of i and then increments it. The only difference in these two programs is that one uses an auto storage class for variable i, whereas the other uses static storage class.
The difference between them is that static variable do not disappear when the function is no longer active. There value persist. If control comes back to the same function again , the static variables have the same values they had last time around.

Description of static program:
In static program, i is declare as static variable so it is initialized to 1 only once. It is never initialized again. During the first call to add(), i is incremented to 2. Because i is static, this value persists. The next time add() is called, i not re-initialized to 1, on the contrary, its old value 2 is still available. This current value of i (i.e. 2) gets printed and then i=i+1; adds 1 to i to get a value of 3. When add() is called the third time , the current value of i (i.e. 3) gets printed and once again i is incremented by 1 and this process going so on till the add() called.
In summarised if the storage class is static, then the statement static int i = 1 is executed only once, irrespective of how many times the same function is called.

External storage class

External variables are differ from remaining other variables. The main features of external variables as following :

Storage	Memory
Keyword	extern
Default initial value	Zero
Scope	Global
Life	As long as the program's execution doesn't come to an end.

External variables are declared outside all functions, yet are available to all functions that care to use them.
Example of external variable or Global variable as following:

/*external variable example program*/
#include<stdio.h>
void add();
void subt();
int main()
{
printf("\ni=%d",i);
add();
add();
subt();
subt();
return 0;
}
void add()
{
int i;
i=i+1;
printf("\nAdding i = %d",i);
}
void subt()
{
int i;
i=i-1;
printf("\nSubtracting i = %d",i);
}

OUTPUT:-

Adding i= 1
Adding i = 2
Subtracting i = 1
Subtracting i = 0

/*program for global variable*/

#include<stdio.h>
int i=50;
void show();
int main()
{
int i=100;
printf("\n%d",i);
show();
return 0;
}
void show()
{
printf("\n%d",i);
}

OUTPUT:-

100
50

/*Another example of external or global variable*/

#include<stdio.h>
int i=5;
int main()
{
extern int j;
printf("\ni=%d \nj=%d",i,j);
int j=10;
return 0;
}

OUTPUT:-

i=5
j=10

Explanation: Because both variables i and j are enjoy as global variable.

Comparison storage classes

In C, storage class provides information about their location and visibility.
C provides four storage classes as:

1. auto storage class

2. register storage

3. extern storage class

4. static storage class

Storage class determines its storage duration, scope and linkage.
Storage duration is the period during which that identifier exists in the memory.
Scope is where the identifier can be referenced in a program.
Linkage determines for a multiple-source file.

Let's summarised all storage classes in C as following as:

Features

Automatic Storage Class

Register Storage Class

Static Storage Class

External Storage Class

Keyword

auto

static

extern

Initial Value

Garbage

Zero

Storage

Memory

CPU register

Memory

Scope

scope limited,local to block

Global

Life

limited life of block,where defined

value of variable persist between different function calls

Global,till the program execution

Memory location

Stack

Segment

Example

void main()

{

auto int i;

printf("%d",i);

}

OUTPUT

124

void main()

{

for(i=1; i<=5 ; i++);

printf("%d ",i);

}

OUTPUT

1 2 3 4 5

void add();

void main()

{

add();

}

void add()

{

static int i=1;

printf("\n%d",i);

i=i+1;

}

OUTPUT

void main()

{

extern int i;

printf("%d",i);

int i=5

}

OUTPUT

FIGURE: Table of Storage classes in C

What is Pointer

What is Pointer?

Pointer is a special variable that represent the address/location of the data item. It provides an alternative way to access the value of a variable.
Pointer is used only store/hold memory address of any variable.

There are some reason to why Pointer used in programs:

1. A pointer able to access a variable that is defined outside the function.

2. Pointer are more efficient in handle the data table.

3. Pointers reduce the length and complexity of the program.

4. Pointer increase the speed of program execution.

5. The use of the Pointer array to character string, result in saving of data storage space in memory.

Pointer Notation

Let's declare a integer variable n which value is 10:

int n = 10 ;

What is this meaning? The above declaration tells the C compiler that:

1. Reserve space in memory to hold the integer value i.e. 65220

2. Associate the name with this memory location i.e. n

3. Store the value at location i.e. 10

and the memory map of above declaration as:

n --------> location name
10 --------> value at location
65220 --------> location/address number

The important point to note in memory map that n's address in memory is a number ( in next chapter we see how it is important? ).

Concept of Pointer

In last chapter ( what is pointer ) , we learn what is the basic of pointer. Now we are learning what is the concept of pointer and how to using it.

In last chapter we declare a variable
int n = 10 ;
and create a memory map, Now we learn how to do this.

Now we print the address of variable through following program:

#include<stdio.h>
int main()
{
int n = 10;
printf("\nAddress of n =%u", &n);
printf("\nValue of n =%d", n);
getch();
return 0;
}

The output of above program:

Address of n = 65220
Value of n = 10

Useful tips i.e. explanations of above programs:

Look at the first printf() statement carefully, it used & ( address of operator ). So & return the address of memory location. In our case, the expression &n return the address of variable n.
%u is used for printing the unsigned integer.

Now, observe carefully the output of the following program:

#include<stdio.h>
int main()
{
  int n = 10;
printf("\nAddress of n =%u", &n);
  printf("\nValue of n =%d", n);
  printf("\nValue of n =%d", *(&n));
getch();
return 0;
}

The output of above program:

Address of n = 65220
Value of n = 10
Value of n = 10

here you can notice that the value of *(&n) is same as printing the value of n.

The expression &n gives the address of the variable n. This address can be collected in a variable, by saying:

int p = &n;

but here 1 problem, p is simple variable so we can't use of variable p.
What is solution?
So here comes the concept of pointer. Now we declare the integer variable p as integer pointer variable:

int *p;
This declaration tells the compiler that p will be used to store the address of an integer value i.e. p points to an integer.

int *p;

Now let's understand the meaning of *. It stand for value at address operator. It return the value at stored at particular address.

The "value at address" operator is also known "indirection operator".

Thus,
int *p; would mean, the value at the address contained in p is an int.

let's check out what you grab:
Q. What will be output of following program?

#include<stdio.h>
int main()
{
int n = 10;
printf("\nOutput of n =%d", n);
printf("\nOutput of *n =%d", *n);
getch();
return 0;
}

Ans.

Output of n = 10
Output of *n = error ( invalid indirection)

Can you understand why second printf() statement generate error? if yes then congratulation... And if you can't figure out then also don't worry because our next chapter is pointer practice session, in this you grab all about pointer.

The reason second printf() statement is generating error because, "value at address ( * )" is used only pointer variable/directly address i.e. "value at address" does not work with simple variable.
In our case n is simple variable and so compiler generate error.

Pointer basic example

We has been discuss about what is pointer and concept of pointer. Now the following program demonstrates the relationship of our pointer discussion.

#include<stdio.h>

int main()

{

int x = 5;

int *y;

y = &x;

printf("\nAddress of x = %u", &x);

printf("\nAddress of x = %u", x);

printf("\nAddress of y = %u", &y);

printf("\nValue of y = %d", y);

printf("\nValue of x = %d", x);

printf("\nValue of x = %d", *(&x));

printf("\nValue of y = %d", *y);

getch();

return 0;

}

The output of above program would be:

Address of x = 2293620

Address of x = 5

Address of y = 2293616

Value of y = 2293620

Value of x = 5

Value of y = 5

/* Screen shot for above program */

Screen-shot for pointer basic example C program

note: the address of variable may be differ because its depend on compiler. I use Bloodshed software "Dev-C++" so you can see that here integer occupy 4 bytes.

The above program summarizes everything that we discussed in what is pointer and concept of pointer chapters. If you don't understand the program output, or the meaning of &x, &y, *y and *(&x), re-read the last 2 chapter of pointer:
What is pointer
Concept of pointer

Now look at the following declaration:

int *n;
char *ch;
float *area;

Here, n, ch and area are declared as pointer variable, i.e. these variable capable of holding addresses.
Keep in mind: Address ( location numbers ) are always whole numbers.
In summarize "we can say pointers are variable that contain addresses and addresses are always whole numbers."

The declaration float *area does not mean that area is going to contain a floating-point value. The meaning is, *area is going to contain the address of a floating-point value.
Similarly, char *ch means that ch is going to contain the address of a char value or in other words, the value at address stored in ch is going to be a char.

Now we know that "Pointer is a variable that contains address of another variable."
Can we further extended it? The answer is Yes, we can. Read in next chapter "Pointer Extended Example".

Pointer Extend Example

Can a pointer variable, itself might be another pointer?
Yes, this pointer would be contains another pointer's address.

The following example/program should should make this point clear:

/*c program for pointer extend example*/

#include<stdio.h>
int main()
{
int x=5;
int *y, **z;

y = &x;
z = &y;

printf("\nAddress of x = %u", &x);
printf("\nAddress of x = %u", y);
printf("\nAddress of x = %u", *z);
printf("\nAddress of y = %u", &y);
printf("\nAddress of y = %u", z);
printf("\nAddress of z = %u", &z);
printf("\nValue of y = %u", y);
printf("\nValue of z = %u", z);
printf("\nValue of x = %u", x);
printf("\nValue of x = %u", *(&x));
printf("\nValue of x = %u", *y);
printf("\nValue of x = %u", **z);

getch();
return 0;
}

The output of the above program would be:

Screen shot for pointer extend example C program

Read above program carefully, the addresses that get output might be something different.
The relationship between x, y and z can be easily summarized as:

Name ---------------- x y z

Value ------------------- 5 2293620 2293616

Address ---------------- 2293620 2293616 2293612

What is the meaning of int x, *y, **z;

Here, x is an ordinary int variable,
y is a pointer to an int i.e. integer pointer,
z is pointer to an integer pointer.

We can extend the above program still further by creating a pointer to a pointer to an integer pointer i.e. ***n
There is no limit on how far can we go on extending this definition. Possibly, till the point we can comprehend it. And that point of comprehension is usually a pointer to a pointer.

What is Function

What is function in C?
A function is a self-contained block of statement that perform a coherent task of some kind.
There are two types of function in C:

1. Library function or In-built function

2. User define function

Structure of function in C program

/* demonstration of function status in program */
#include<stdio.h>
void disp(); /* function prototype declaration */
int main()
{
  disp();    /*function calling*/
printf("C is Awesome!!!");
return 0;
}
void disp() /* function definition */
{
printf("Hi, ");
}

The output of above program would be:

Hi, C is Awesome!!!

Let's grab some useful info from the above program:
In above program we have 2 function:
main()
disp()

Here you can see and thought:
1. why main() is used only once in program?
2. why disp() is used three times in program?

The answer of first question is "if a c program contains only one function then it must be main()." i.e. every C program must have main() function.

The answer of second question: let's understand the meaning of every disp() in program:

void disp();
this is the first disp() that used in program. It is function prototype.
This prototype tells the compiler that as:
What is function type ( i.e. void or not ),
What is name of function( i.e. in our program function name is disp)
Both parenthesis () indicate that disp is function.
keep in mind: void word indicating that "nothing return".

disp();
this is the second disp() that used in program. It is function calling.
Every calling function main work is as:
when compiler reached at calling function disp(); program control passes to the function disp(), (i.e. activity of main() is temporary suspend ), when disp() function runs out all his statement execute, the control returns to the main() function and begins executing code at the exact point where it is left off.

void disp()
{
printf("Hi, ");
}

this is the third disp() that used in program. It is function definition.
In function definition we can used all C language keywords, operators, variable etc.
In above program recently we have only 1 printf(); statement.

Let's exercise, what we learn:

/*exercise of function calling C program*/
#include<stdio.h>
void fun1();
void fun2();
void fun3();
int main()
{
printf("\nI am in main function!!");
fun1();
fun2();
fun3();
return 0;
}
void fun1()
{
printf("\nI am in fun 1");
}

void fun2()
{
printf("\nI am in fun 2");
}

void fun3()
{
printf("\nI am in fun 3");
}

The output of above program would be:

I am in main function!!
I am in fun 1
I am in fun 2
I am in fun 3

C Standard Library Inbuilt Function

With every C compiler, a large set of useful string handling library function are provided.
Below lists the more commonly used functions along with their name and features as:

Function name	Features
strlen()	Calculate length of string
strcpy()	Copy from one string to another
strncpy()	Copies first n characters of one string into another
strcat()	Appends one string at the end of another
strncat()	Appends first n characters of a string at the end of another
strcmp()	Compares two string
strncmp()	Compares first n characters of two string
strcmpi()	Compares two string with ignore the case
stricmp	Compares two string with ignore the case(identical to strcmpi)
strnicmp	Compares first n characters of two string with ignore the case
strlwr	Convert a string to lowercase
strupr	Convert a string to uppercase
strrev	Reverse string
strdup	Duplicate a string
strchr	Finds first occurrence of a given character in a string
strrchr	Finds last occurrence of a given character in a string
strstr	Finds first occurrence of a given string in another string
strset	Sets all characters of string to a given character
strnset	Sets first n characters of a string to a given character

Table: Standard Library String Function in C Language

(For syntax, example and use of above function, click at related function name.)

User Define Function

What is User Define Function?
A function that is declare, calling and define by the user is called user define function.
Every user define function has three parts as:

1. Prototype or Declaration

2. Calling

3. Definition

1. Prototype or Declaration

Prototype/declaration set the outline of function like as:

function is something returning or not?

what is function name?

what would be the nature of parameter?

how much parameters used in function?

This is generally written at top of program like as after or before the main() function.

syntax:

return_data_type function_name(data_type parameter, ......);

Description of syntax:

In above syntax "return_data_type" may be two types:

if return_data_type is void: This mean that our function nothing return.

if return_data_type is other like as int, float, double etc. then it would be return as int, float, double etc. respectively.

for example:

int factorial(int num); //it would return a integer value.

void display(int num); //it would nothing return.

In above syntax "function_name" means that the name of function which we want to make.

for example:

int myfunction(int i);

In above syntax "data_type parameter" means that first write down the data type( int, float, double, long, char ) and after write down the name of related parameter/argument/variable. It is may be one, two and so on as the requirement of function.

for example:

int sum(int x, int y);

int myfunction(int name);

In Prototype or Declaration of function, we can write only the name of data type, not require the name of parameter/argument( it is optional ).

for example:

int sum(int , int ); //it would return a integer value.

int myfunction(int ); // this is valid and correct

int myfunction(char ); // this is valid and correct

2. Calling

The calling part of function work as:

It is call the function.

It forward the control of main() to user define function and vice versa.

The calling is generally written as middle of program after grab all related argument.

syntax:

//if return type is void:

function_name(actual argument/parameter);

//if return type is not void:

return_parameter=function_name(actual argument/parameter);

for example:

display(num); //void calling function- display

result=sum(x, y) //return calling function-sum

f=factorial(num) //return calling function- factorial

ex=myfunction(number) //return calling function - myfunction

3. Definition

The "definition" part is the heart of function.

What will function do? It define the all function body.

The definition part must be exist at outside of main() function. i.e. it is written after making all the program.

syntax:

//if return type is void:

function_name(data_type argument/parameter)

{

statement 1;

statement n;

}

//if return type is not void:

return_data_type function_name(data_type parameter)

{

statement 1;

statement n;

return ( any_return_value);

}

example:

int sum(int x, int y)

{

int res;

res = x+y;

return(res);

}

A complete example of user define function:

/*demonstration of user define function-sum*/

#include<stdio.h>

int sum(int , int); //Prototype or Declaration

int main()

{

int x,y,result;

printf("Enter value of x and y: ");

scanf("%d %d", &x, &y);

result=sum(x, y); //calling of function-sum

printf("Sum of %d + %d = %d",x,y,result);

return 0;

}

//Definition of function sum

int sum(int a, int b)

{

int res;

res = a + b;

return ( res );

}

The output of above program would be:

Figure: Screen shot for user define function
sum C program

Array in C

Before you kick start to reading array, you should understand why array concept is comes? How it is requires in C?

Let's read following program:

#include<stdio.h>

int main()

{

int r;

r=1;

r=2;

printf("The value of r = %d",r);

getch();

return 0;

}

The output of above program would be:

The value of r = 2

So, you can understand that when the value 2 is assigned into r, the earlier value of r (i.e. 1) is lost. Thus the ordinary variables are capable of holding only one value at a time.

What we do if we would want to store more than one value at a time in a single variable?

Here, the comes the concept of array.

What is array?

1. Array is a collection of similar elements.

2. The first element in the array is numbered 0, so the last element is 1 less than the size of the array.

3. An array is also known as a subscripted variable.

4. Before using an array, its type and dimension must be declared.

5. The array elements are always stored in contiguous memory locations. This is a very important features of array.

Thus, an array is collection of similar elements. These similar elements could be all ints, or all floats, or all chars.

Array of characters is called a string whereas an array of ints or floats is called simply an array.

Keep in mind that all elements of any array must be the same type. i.e. cannot have an array of 10 numbers, of which 5 are ints and 5 are floats.

1.  Array declaration and Initialization

2. Bounds Checking

3. Array and function

4. Array and Pointers

 Array of pointers

 2-d Array

 3-d Array

C Preprocessor

What is C Preprocessor?

It is a program that processes our source program before it is passed to the compiler.

Preprocessor command also known as directives.

Each preprocessor directory is begin with a # symbol.

It is can be placed anywhere in the program but are most often placed at the beginning of a program.

The C program is often known as 'Source Code'. The preprocessor works on the source code and creates 'Expanded Source Code'.
If the source code is stored in a file say MYPROG.C, then the expanded source code gets stored in a file MYPROG.I. It is this expanded source code that is sent to the compiler for compilation.

Example of some preprocessor directives as:

Macro Expansion
Conditional compilation
File inclusion
Miscellaneous directives

We discuss all above preprocessor in detailed one by one.

Macro Expansion

What is macro?

Let's understand macro using following program:

/*c program for macro expansion*/

#include<stdio.h>

#define LENGTH 3

#define WIDTH 2

int main()

{

int r,c;

for(r=1; r<=LENGTH; r++)

{

for(c=1; c<=WIDTH; c++)

printf("%d%d",c,r);

printf("\n");

}

getch();

return 0;

}

The output of above program would be:

Figure: Screen shot of macro C program

In above program, instead of writing 5 in the for loop we are writing it in the form of text as LENGTH and WIDTH, which have already been defined before main() through the statement.

#define LENGTH 3

#define WIDTH 2

This statement is called 'macro definition' or macro.

LENGTH and WIDTH in the above program are often called 'macro templates' , whereas 5 and 3 are called their corresponding 'macro expansions'.

What is reason of using macro in the program?

Macro makes the program easier to read.

For example: if the phrase "%ls[$2]!@" cause the screen to clear, but which would you find easier to understand in the middle of your program "%ls[$2]!@" or "CLRSCREEN"?

#define CLRSCREEN "%ls[$2]!@"

Macro makes the easyness if we want to change the vale of constant in program. We can change value values of a constant at all the places in the program by just making a change in the #define directive.

This conversion may not matter for small programs shown above, but with large programs, macro definitions are almost indispensable.

Now you will be thinking, there are any similarity in macro and variable? Can i use variable as macro?

(i recommended, before you read next line, you should think about macro and variable properties.)

After thinking you will be find that we also use variable as macro. Then why not use it?

Why the variable is not using as macro because:

1. Variable may inadvertently get altered somewhere in the program. so it's no longer a constant that you think it is.

2. Variable is inefficient, since the compiler can generate faster and more compact code for constant than it can for variables.

3. Using a variable for what is really a constant encourages sloppy thinking and makes the program more difficult to understand: if something never changes, it is hard to imagine it as a variable.

Macro Rules and Example

Macro without argument example

A #define directive is many a time used to define operators as shown below:

#include<stdio.h>
#define OR ||
#define AND &&
int main()
{
int p=10,q=20,r=30;
if((p==10) AND (q<25 OR r>=50))
printf("You are winner!!");
else
printf("You are loser!!");
getch();
return 0;
}

The output of above program would be:

Figure: Screen shot of shows macro uses in C program

A #define directive could be used even to replace a condition as:

#include<stdio.h>
#define OR ||
#define AND &&
#define RESULT ((p==10) AND (q<25 OR r>=50))
int main()
{
int p=10,q=20,r=30;
if(RESULT)
printf("You are winner!!");

else
printf("You are loser!!");
getch();
return 0;
}

The output of above program would be:

Figure: Screen shot of shows macro uses in C program

A #define directive could be used to replace even an entire C statement.

#include<stdio.h>
#define DISPLAY printf("Yes, I got iT");
int main()
{
DISPLAY;
getch();
return 0;
}

The output of above program would be:

Figure: Screen shot for macro example C program

Macro with argument example

#include<stdio.h>
#define SQUARE(p) (p*p)
int main()
{
int n,result;
printf("Enter any number: ");
scanf("%d", &n);
result = SQUARE(n);
printf("Square of %d is %d",n,result);
getch();
return 0;
}

The output of above program would be:

Figure: Screen shot of macro square C program

Keep in mind some following point, when you create macro

1. If there are two or more macro expansions then, entire macro expansions should be enclosed within parentheses.

Example:

#define SQUARE(p) p*p //wrong

#define SQUARE(p) (p*p) //right

2. There should be not a blank between the macro template and its argument while defining the macro.

Example:

#define SQUARE (p) p*p //wrong

#define SQUARE(p) (p*p) //right

3. Macro can be split into multiple lines, with a '\'(back slash) present at the end of each line.

Example:

#include<stdio.h>

#define MYPROG for(c=1; c<=10; c++) \

{ \

if(c==5) \

printf("Good C blog."); \

}

int main()

{

int c;

MYPROG

getch();

return 0;

}

The output of above program would be:

Figure: Screen shot for macro split C program

File Inclusion

The first preprocessor directive is macro and the second preprocessor directive is file inclusion.
File inclusion causes one file to be included in another.

#include "filename"

What is the meaning of above syntax?
It is simply causes the entire contents of filename to be inserted into source code at that point in the program.

Why file inclusion is used?

If we have a very large program, the code is best divided into several different files, each containing a set of related functions. It is a good programming practice to keep different sections of a large program separate. These files are #included at the beginning of main program file.
There are some functions and some macro definitions that we need almost in all program that we write. These commonly needed functions and macro definitions can be stored in a file, and that file can be included in every program we write, which would add all the statements in this file to our program as if we have typed them in.

There are two way to write #include statement as:

1. #include "myfile.h"
This command would look for the file myfile.h in the current directory as well as the specified list of directories as mentioned in the include search path that might have been setup.

2. #include<myfile.h>
This command would look for the file myfile.h in the specified list of directories only.

Conditional Compilation

What is conditional compilation?
You can understand it by its name i.e. a program is compiling according condition.
In other word, we can, if we want, have the compiler skip over part of a source code by inserting the preprocessing commands #ifdef and #endif, which have the general form:

#ifdef macroname
statement 1;
statement 2;
statement 3;
statement 4;
#endif

if macroname has been #defined, the block of code will be processed as usual, otherwise not.

Preprocessor directives

The #if directive can be used to test whether an expression evaluates to a nonzero value or not. If the result of the expression is nonzero, then subsequent lines upto a #else, #elif or #endif are compiled, otherwise they are skipped.

Syntax of #if directive as:

#if LABEL == 10
statement 1;
statement 2;
#else
statement 3;
statement 4;
statement 5;
#endif

If we so desire, we can have nested conditional compilation directives.

#undef directive

Sometimes, it may be desirable to cause a defined name to become 'undefined'. This can be accmplished by means of the #undef directive.
Syntax: #undef macro_temp_name
example: #undef TEST

#pragma Directive

This is a special directive that we use to turn on or off certain features. Pragma vary from one compiler to another.
Turbo c/c++ compiler has got a pragma that allows you to suppress warnings generated by the compiler.
Some pragmas directives as following:

#pragma startup and #pragma exit
#pragma warn

Programming

Tuesday, January 5, 2016

C Basic

Keywords in C

Logical Operator

Bitwise operators

Arithmetic Operator

Relational Operator

Sizeof operator

Intro if-else

Forms of if-else

More if-else

for Loop

do-while loop

Odd Loop

break statement

continue statement

switch-case statement

goto statement

Flowchart for switch-case

Storage classes

Automatic Storage Class

Register Storage Class

Static Storage Class

External storage class

Concept of Pointer

Pointer basic example

Pointer Extend Example

C Standard Library Inbuilt Function

Macro Rules and Example

File Inclusion

Conditional Compilation

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