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A loop statement allows a program to execute a statement(s) multiple times which provides easier and flexible programming. C has three loop statements:

  • While loop
  • Do-While loop
  • For loop

The While Loop:

While loop allows a set of statements to be executed repeatedly until a given condition is true. The While loop can be viewed as a repeating if statement.

Syntax

while (condition) {
  statements;
}

Flow Diagram:

C While Loop

In below mentioned example, program uses while loop to sum all integers from 1 to 5.

#include <stdio.h>
 
int main (){
    int i = 1;
    int sum = 0;
    while (i < 6){
        sum = sum + i;
        i = i+1;
    }
    printf("%i",sum);
    return 0;
}

The output of the above code will be:

15

The Do-While Loop:

The Do-While loop in C is a variant of while loop which execute statements before checking the conditions. Therefore the Do-While loop executes statements at least once.

Syntax

do {
  statements;
}
while (condition);

Flow Diagram:

C While Loop

In the below example, even if the condition is not fulfilled, the do-while loop executes the statements once.

#include <stdio.h>
 
int main (){
  int i = 10;
  int sum = 0;
  do {
    sum = sum + i;
    i = i+1;
  }
  while (i < 6);
  printf("%i",sum);
  return 0;
}

The output of the above code will be:

10

5