C - While Loop

A loop statement allows a program to execute a given block of codes repeatedly under a given condition. This enables a programmer to write programs in fewer lines of code and enhance the code readability. C has following types of loop to handle the looping requirements:

while loop
do-while loop
for loop

The While Loop

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

Syntax

while (condition) {
  statements;
}

Flow Diagram:

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:

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:

In the example below, 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: