While Loops Stop Only When the Body Makes Them Stop

A while loop checks its condition before every repetition

A while loop tests a Boolean condition before it runs its body. In the countdown, count starts at 3, so the condition count > 0 is true and the body runs. The body prints count and then decreases it. After the body finishes, execution returns to the condition instead of moving directly to the line after the loop.

int count = 3;

while (count > 0) {
    cout << count << "\n";
    count--;
}

cout << "Done\n";

The line while (count > 0) contains the condition. The statements between the braces are the loop body. The exact order is: test count > 0, run the body only when the test is true, then return to the test. When the test is false, the body is skipped and execution continues with cout << "Done\n".

The countdown reaches 1 only because count changes after each print

The first condition check sees count equal to 3, so the body prints 3 and count-- changes count to 2. The next check sees 2, prints it, and changes count to 1. The next check sees 1, prints it, and changes count to 0. Each pass changes the value that the next condition check will read.

The value in the first column is the value available before the condition is tested. The value in the last column is the value left for the next check. The post-decrement does not change the already printed number, so the body prints 3 before changing count to 2, then prints 2 before changing count to 1.

A condition that stays true makes the same loop run forever

The while statement supplies repetition, not progress. The body must change something that can eventually make the condition false. If the decrement is removed, the body still prints count, but nothing changes count. The first check sees 3, the body prints 3, and the next check sees 3 again.

int count = 3;

while (count > 0) {
    cout << count << "\n";
}

cout << "Done\n";

This loop does not reach the line that prints Done. It keeps taking the true path because count remains 3, so it keeps printing 3. The loop does not automatically decrement, increment, or otherwise update a control variable. Those changes must be written in the body.

while (count > 0) {
    cout << count << "\n";
    
}

The false check exits the loop without running the body again

After the body prints 1, count-- changes count from 1 to 0. The loop then performs one final condition check. Because count > 0 is false when count is 0, the body does not run again, so 0 is not printed. Execution leaves the loop and prints Done, with count still equal to 0.

condition check: count = 3, true
print: 3
count becomes 2

condition check: count = 2, true
print: 2
count becomes 1

condition check: count = 1, true
print: 1
count becomes 0

condition check: count = 0, false
print: Done

The final failed check is still part of the loop's control flow, but it is not another repetition. A true check permits one body pass. A false check skips the body and sends execution to the first statement after the loop. That is why the output ends with Done rather than 0.