The do-while loop
- C course
- Beginner
- Lesson 44/116
- 4 min
Learn loops that run at least once with do-while.
The do-while loop
The do-while loop runs the body at least once, then checks the condition. This is useful for cases like menus where the question must be asked at least once.
int n = 0;
do {
printf("%d\n", n);
n++;
} while (n < 3);Here even with n=0 the body runs once. Output: 0 1 2. Unlike while, the condition is checked at the end; the semicolon is mandatory.
Semicolon in do-while
In do-while, the semicolon at the end of the while line is mandatory. Forgetting it is a common compile error.
int choice;
do {
printf("Continue? 1/0: ");
scanf("%d", &choice);
} while (choice == 1); // semicolon requiredThis example loops as long as the user enters 1. When they enter 0 it ends. The return value of scanf is an int; not used here, but you learned the logic.
Practice 0 to 2 with do-while
Write a C program. Declare int n = 0;. Write a do { ... } while (n < 3); loop; in the body include printf("%d\n", n); and n++;. Put #include <stdio.h> at the top.
Starter code
#include <stdio.h>
int main(void) {
// Declare n, print with do-while
return 0;
}Sample solution
#include <stdio.h>
int main(void) {
int n = 0;
do {
printf("%d\n", n);
n++;
} while (n < 3);
return 0;
}Expected output
0 1 2
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the loop features
| Term | Meaning |
|---|---|
for |
Counted |
while |
Condition first |
do-while |
Condition last |
at least once |
do-while |
2 How many times does do-while run?
int n = 10;
do {
printf("%d", n);
} while (n < 5);- At least once Correct answer
- Never
- 5 times
- Infinite
Explanation: Even with a false condition the body runs at least once.
3 Complete the do-while
do {
n++;
} ____ (n < 5);do {
n++;
} while (n < 5);Explanation: do-while checks the condition with while after the body.