while Loop

The while loop repeats a block of code as long as a condition remains true. Use it when you don’t know in advance how many times the loop will run.

Basic Syntax

while (condition) {
    // body, runs while condition is true
}

The condition is checked before each iteration. If it is false from the start, the body never runs.

int i = 0;
while (i < 5) {
    print(i);
    i = i + 1;
}
// Output: 0 1 2 3 4

Counting Down

int count = 5;
while (count > 0) {
    print(count);
    count = count - 1;
}
// Output: 5 4 3 2 1

Reading an Array

int[] arr = [2, 4, 6, 8];
int i = 0;
while (i < 4) {
    print(arr[i]);
    i = i + 1;
}
// Output: 2 4 6 8

Infinite Loop

If the condition never becomes false, the loop runs forever:

while (true) {
    // runs forever, use break or return to exit
}

break in while

Exit the loop immediately:

int i = 0;
while (i < 10) {
    if (i == 3) { break; }
    print(i);
    i = i + 1;
}
// Output: 0 1 2

continue in while

Skip to the next iteration. Unlike for, the update must happen before the continue, or it gets skipped too:

int i = 0;
while (i < 5) {
    i = i + 1;          // update happens first
    if (i == 3) { continue; }
    print(i);
}
// Output: 1 2 4 5  (3 skipped)

If you put continue before the update, you create an infinite loop, because the counter never advances:

int i = 0;
while (i < 5) {
    if (i == 3) { continue; }  // i never changes when i==3!
    print(i);
    i = i + 1;
}
// WARNING: infinite loop when i reaches 3

Nested while

int i = 1;
while (i <= 3) {
    int j = 1;
    while (j <= 3) {
        print(i * j);
        j = j + 1;
    }
    i = i + 1;
}

Popcount Example (Counting 1-bits)

int popcount(int n) {
    int count = 0;
    while (n != 0) {
        count = count + (n & 1);
        n = n >> 1;
    }
    return count;
}

int main() {
    print(popcount(7));   // 3, binary 111
    print(popcount(256)); // 1, binary 100000000
    return 0;
}

Advanced: while (true) with break

When the exit condition is easier to express inside the loop than at the top, a common idiom is an intentional infinite loop with a break:

int n = 100;
int steps = 0;
while (true) {
    if (n == 1) { break; }          // exit condition, mid-loop
    if (n % 2 == 0) { n = n / 2; }
    else { n = 3 * n + 1; }
    steps = steps + 1;
}
print(steps);                        // Collatz steps to reach 1

This keeps the loop going until some event happens, rather than forcing every exit reason into a single top-of-loop condition. At least one break (or return) must be reachable, or the loop never ends.

When to Use while vs for

Use for when…	Use while when…
You know the number of iterations	The number depends on a dynamic condition
You’re iterating over an array by index	You’re waiting for a state change
You have a clear init/condition/update pattern	You just need “keep going while X”

What’s Next?

• See do-while loops for a guaranteed first iteration
• Learn about functions to organize your code