The while loop

Learn loops that run while a condition holds with while.

The while loop

The while loop runs as long as the condition is true. The condition is checked first; if false, the body never runs.

int n = 5;
while (n > 0) {
    printf("%d\n", n);
    n--;
}

Here n starts at 5, decrements each iteration, and the loop ends when n reaches 0. Output: 5 4 3 2 1. Without n-- in the body the loop would be infinite; be careful.

for vs while

Any for loop can be written as a while. for is preferred when the iteration count is known; while when the condition is more dynamic.

// with for
for (int i = 0; i < 5; i++) { ... }

// the same with while
int i = 0;
while (i < 5) { ...; i++; }

Both work identically. With for the counter is declared in one line; with while it spreads across four lines. Which to use depends on context.

Exercise Count down from 5

Write a C program. Declare int n = 5;. Use a while (n > 0) loop to print printf("%d\n", n); and decrement with n--;. Put #include <stdio.h> at the top.

Show example solution

#include <stdio.h>

int main(void) {
    int n = 5;
    while (n > 0) {
        printf("%d\n", n);
        n--;
    }
    return 0;
}

Test yourself

Complete the condition

while (____ > 0) {
    printf("%d", n);
    n--;
}

Show answer

while (n > 0) {
    printf("%d", n);
    n--;
}

When does while (n > 0) end?
```
while (n > 0) {
    n--;
}
```
- When n=1
- When n=5
- Never
- When n=0
Show answer

When n=0 — When n reaches 0 the condition becomes false and the loop ends.
Match the loop types

for

Counted loop
while

Conditional loop
i++

Increment
n--

Decrement

Next lesson: The do-while loop

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