Loop In C Language

Loop In C Language 

A loop statement allows us to execute a statement or group of statements multiple times. Given below is the general form of a loop statement in most of the programming languages −

C programming language provides the following types of loops to handle looping requirements.

Sr.No.	Loop Type & Description
1	while loop Repeats a statement or group of statements while a given condition is true. It tests the condition before executing the loop body.
2	for loop Executes a sequence of statements multiple times and abbreviates the code that manages the loop variable.
3	do...while loop It is more like a while statement, except that it tests the condition at the end of the loop body.
4	nested loops You can use one or more loops inside any other while, for, or do..while loop.

While Loop in C

A while loop is the most straightforward looping structure. While loop syntax in C programming language is as follows:

Syntax of While Loop in C:

while (condition) {
             statements;
}

It is an entry-controlled loop. In while loop, a condition is evaluated before processing a body of the loop. If a condition is true then and only then the body of a loop is executed. After the body of a loop is executed then control again goes back at the beginning, and the condition is checked if it is true, the same process is executed until the condition becomes false. Once the condition becomes false, the control goes out of the loop.

After exiting the loop, the control goes to the statements which are immediately after the loop. The body of a loop can contain more than one statement. If it contains only one statement, then the curly braces are not compulsory. It is a good practice though to use the curly braces even we have a single statement in the body.

In while loop, if the condition is not true, then the body of a loop will not be executed, not even once. It is different in do while loop which we will see shortly.

Following program illustrates while loop in C programming example:

#include<stdio.h>
#include<conio.h>
int main()
{
	int num=1;	//initializing the variable
	while(num<=10)	//while loop with condition
	{
		printf("%d\n",num);
		num++;		//incrementing operation
	}
	return 0;
}

Output:

1
2
3
4
5
6
7
8
9
10

Do-While loop in C

A do…while loop in C is similar to the while loop except that the condition is always executed after the body of a loop. It is also called an exit-controlled loop.

Syntax of do while loop in C programming language is as follows:

Syntax of Do-While Loop in C:

 do {
  statements
} while (expression);

As we saw in a while loop, the body is executed if and only if the condition is true. In some cases, we have to execute a body of the loop at least once even if the condition is false. This type of operation can be achieved by using a do-while loop.

In the do-while loop, the body of a loop is always executed at least once. After the body is executed, then it checks the condition. If the condition is true, then it will again execute the body of a loop otherwise control is transferred out of the loop.

Similar to the while loop, once the control goes out of the loop the statements which are immediately after the loop is executed.

The critical difference between the while and do-while loop is that in while loop the while is written at the beginning. In do-while loop, the while condition is written at the end and terminates with a semi-colon (;)

The following loop program in C illustrates the working of a do-while loop:

Below is a do-while loop in C example to print a table of number 2:

#include<stdio.h>
#include<conio.h>
int main()
{
	int num=1;	//initializing the variable
	do	//do-while loop 
	{
		printf("%d\n",2*num);
		num++;		//incrementing operation
	}while(num<=10);
	return 0;
}

Output:

2
4
6
8
10
12
14
16
18
20

For loop in C

A for loop is a more efficient loop structure in ‘C’ programming. The general structure of for loop syntax in C is as follows:
Syntax of For Loop in C:
for (initial value; condition; incrementation or decrementation ) 
{
  statements;
}
The initial value of the for loop is performed only once.
The condition is a Boolean expression that tests and compares the counter to a fixed value after each iteration, stopping the for loop when false is returned.
The incrementation/decrementation increases (or decreases) the counter by a set value.
Following program illustrates the for loop in C programming example:
#include<stdio.h>
int main()
{
	int number;
	for(number=1;number<=10;number++)	//for loop to print 1-10 numbers
	{
		printf("%d\n",number);		//to print the number
	}
	return 0;
}
Output:
1
2
3
4
5
6
7
8
9
10
The above program prints the number series from 1-10 using for loop.