Loops in C

Types of Loops in C

1. while loop
2. do-while loop
3. for loop
4. Nested loop

1. while loop:
The while statement is used to execute a single statement or block of statements repeatedly until the given condition is TRUE. It is also known as Entry control loop.

Syntax

control_variable_initialization;  
while(condition)  
{  
  statement(s);  
  control_variable_update;  
}  

2. do-while loop:
The do-while loop is similar to that of the while loop, but the main difference is while loop evaluates the condition first and then executes the statements, whereas the do-while loop executes the statements first before evaluating the condition. It is also known as Exit control loop.

Syntax

control_variable_initialization;  
do  
{  
  statement(s);  
  control_variable_update;  
}  
while(condition);  

3. for loop:
It is a pre-tested loop and is used when the number of repetitions(iterations) is known. The syntax of for-loop consists of three parts: control variable initialization, condition, and control variable update. These three parts are separated by a semicolon(;).

Syntax

for(control_variable_initialization; condition; control_variable_update)  
{  
  statement(s);  
}  

C program to find the sum of first 50 natural numbers.

#include<stdio.h>  
#include<conio.h>  
void main()  
{  
  int i,sum=0;  
  for(i=1;i<=50;i++) 
  sum=sum+i;   printf("The sum of first 50 natural numbers is %d", sum);  
  getch();  
}  

Output:
The sum of first 50 natural numbers is 1275

Note: Curly braces are optional if body of loop consists of single statement.

4. Nested loop:
A nested loop is a loop within a loop, an inner loop within the body of an outer one.

Syntax

for(initialization; condition; increment/decrement)  
{  
  statement(s);  
  for(initialization; condition; increment/decrement)  
  {  
  statement(s);  
 ...........  
  }  
 ...........  
}