C While Loops

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In programming, a loop is used to repeat a block of code until the specified condition is met.

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While Loops

The while loops through a block of code as long as a specified condition is true:

Syntax

while (condition) {  
  // code block to be executed
}

How while loop works?

• The while loop evaluates the testExpression inside the parentheses ().
• If testExpression is true, statements inside the body of while loop are executed. Then, testExpression is evaluated again.
• The process goes on until testExpression is evaluated to false.
• If testExpression is false, the loop terminates (ends).

Note: testExpression it’s made by C Comparison Operators and C Logical Operators.

For loop Flowchart

Example:

// Print numbers from 1 to 5
 
#include <stdio.h>
int main() {
  int i = 1;
    
  while (i <= 5) {
    printf("%d\n", i);
    ++i;
  }
 
  return 0;
}

Output: 1 2 3 4 5

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Do…While Loop

The body of do...while loop is executed at least once. Only then, the test expression is evaluated.

Syntax

do {
  // the body of the loop
}
while (testExpression);

How do…while loop works?

• The body of do...while loop is executed once. Only then, the testExpression is evaluated.
• If testExpression is true, the body of the loop is executed again and testExpression is evaluated once more.
• This process goes on until testExpression becomes false.
• If testExpression is false, the loop ends.

Example:

// Program to add numbers until the user enters zero
 
#include <stdio.h>
int main() {
  double number, sum = 0;
 
  // the body of the loop is executed at least once
  do {
    printf("Enter a number: ");
    scanf("%lf", &number);
    sum += number;
  }
  while(number != 0.0);
 
  printf("Sum = %.2lf",sum);
 
  return 0;
}

Output: Enter a number: 1.5 Enter a number: 2.4 Enter a number: -3.4 Enter a number: 4.2 Enter a number: 0 Sum = 4.70

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