Beginner 15 min read

While Loops

By the end of this lesson, you'll be able to:

Write a while loop with a condition checked before each pass
Explain why a while loop needs something inside it that eventually makes the condition false
Choose while over for when the number of iterations isn't known in advance

Prerequisites: "Enhanced For Loops"

The shape

Integer stock = 20;

while (stock > 0) {
    stock -= 3;
    System.debug('Stock remaining: ' + stock);
}

Unlike a for loop, there's no built-in counter — you're fully responsible for making sure something inside the loop eventually makes the condition false. Here that's stock -= 3, which shrinks stock toward (and past) zero.

A real business example: Telecom (Call Queue)

Integer callsInQueue = 7;

while (callsInQueue > 0) {
    System.debug('Connecting next caller. Calls remaining: ' + callsInQueue);
    callsInQueue--;
}

System.debug('Queue cleared.');

A call center doesn't know how many calls will be in the queue at any moment — that number changes constantly. while fits this naturally: keep connecting callers as long as there are calls waiting.

Common mistakes

Forgetting to change the condition variable inside the loop. If stock was never decremented above, stock > 0 would stay true forever, and Apex would eventually hit a governor limit and throw an error rather than actually loop infinitely.
Using while when for fits better. If you already know the exact number of iterations up front, a for loop usually communicates that more clearly than a while loop with a manually managed counter.

Exercise

Declare Integer countdown = 5. Write a while loop that debugs countdown and decreases it by 1 each time, stopping once it reaches 0.

Show hint

while (countdown > 0) { ...; countdown--; }

APEX

While Loops Quiz

1. What must a while loop's body eventually do?

Change something so the condition eventually becomes false Nothing — while loops end automatically Call another loop Return a value

My Notes

Questions about this lesson

No questions yet — be the first to ask.

Summary

A while loop keeps running as long as its condition is true, checked fresh before every pass — the right tool when you don't know in advance how many times you'll need to repeat.

← Enhanced For Loops Do-While Loops →