The while loop

Learn loops that run while a condition holds with while.

The while loop

The construct that repeats while a condition holds is the while loop. Its form is while (condition) { ... }; the condition is checked at the start of each iteration and, when false, the loop ends.

For example int count = 0; while (count < 3) { std::cout << count; count++; } prints 0, 1 and 2. You must write the increment yourself; forgetting it produces an infinite loop. while is preferred over for when the number of iterations is not known in advance.

while vs for

while and for can often replace each other. The rule of thumb: pick for when you know the number of iterations, while when you do not. while feels more natural when reading user input or going until the end of a file.

Writing while (true) creates an infinite loop; it keeps running until you exit with break. This pattern is common in menus and event loops. Used carelessly, however, it can freeze the program.

Exercise Print 0, 1, 2 (while)

The count variable is set to 0. Inside a while (count < 3) loop print count with std::cout << count; and increase it with count++. The output must be 012.

Show example solution

#include <iostream>

int main() {
    int count = 0;
    while (count < 3) {
        std::cout << count;
        count++;
    }
    std::cout << std::endl;
    return 0;
}

Test yourself

Match each while part to its role

while (cond)

Condition at top
count++

Increment in body
count < 3

Continue condition
{ ... }

Loop body
What kind of loop is while (true)?
```
while (true) { ... }
```
- Never runs
- Runs once
- Compile error
- Infinite loop
Show answer

Infinite loop — The condition is always true so the loop runs forever without a break.

Write the while condition

int count = 0;
while (____) { count++; }

Show answer

int count = 0;
while (count < 3) { count++; }

Next lesson: The do-while loop

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