Beginner · C PROGRAMMING

While and do while

What you will learn

Use condition-controlled repetition.

Understand the concept

while checks before the body and can run zero times. do while checks afterward and runs at least once. Update a value involved in the condition so that the loop can finish.

Read the example

The complete program appears below. Read it first, predict the output, then run it.

Expected output

3
2
1
Finished

Practise

Start remaining at zero. Explain why only the do-while body prints.

Common mistake

Forgetting the decrement can create an infinite loop. The do-while statement requires a final semicolon.

Lesson discussion

#include <stdio.h>

int main(void) {
    int remaining = 3;
    while (remaining > 0) {
        printf("%d\n", remaining);
        --remaining;
    }
    do {
        puts("Finished");
    } while (remaining > 0);
    return 0;
}

PRACTICE LAB

Read. Edit. Run.

C source · .c

Experiment with the program below. Your code and input are sent to the selected compiler only when you run it.

Compiler

C source

Tab indents · Shift+Tab unindents · Esc then Tab leaves the editor · Ctrl/Cmd+Enter runs · Ctrl/Cmd+S saves a draft

Changes save automatically to your account.

Standard input

Input / output example

Example input

No input required.

Expected output for the original program

3
2
1
Finished

Output will appear here.

While and do while

What you will learn

Understand the concept

Read the example

Expected output

Practise

Common mistake

Lesson discussion

Read. Edit. Run.

Input / output example

Debugging Lab

Interactive Memory Visualizer

Stack frames

Memory and pointers

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