C While Loop

The while Loop

A while loop checks a condition before every pass. As long as the condition evaluates to true (any non-zero value), the code inside the curly braces runs. When the condition becomes false, the loop stops and the program continues after the loop.

#include <stdio.h>

int main() {
  int i = 0;
  while (i < 5) {
    printf("i is %d\n", i);
    i++;
  }
  return 0;
}

In the example above, i starts at 0. The condition i < 5 is checked each time. We print the value, then i++ increases i by 1. After i reaches 5 the condition is false, so the loop ends. The output is the numbers 0, 1, 2, 3, and 4 each on their own line.

• The condition is tested first, before the body runs.
• If the condition is false at the start, the body never runs at all.
• Use a counter variable to control how many times the loop repeats.

#include <stdio.h>

int main() {
  int number = 1;
  int sum = 0;
  while (number <= 5) {
    sum += number;
    number++;
  }
  printf("The sum is %d\n", sum);
  return 0;
}

Here we add 1 + 2 + 3 + 4 + 5 by looping while number is 5 or less. Each pass adds number to sum, then increases number. The program prints: The sum is 15.