Loops

Enemy 1 of 5

The for loop, piece by piece

Loops let a program repeat a block of code without you writing it out by hand for every repetition — which matters not just for saving typing, but because a change to repeated logic only needs to happen in one place instead of everywhere it was copy-pasted.

A for loop packs three pieces into its parentheses, separated by semicolons: an initializer that runs once before the loop starts (var i = 0), a condition checked before every iteration that keeps the loop going as long as it's true (i < 3), and an update that runs after every iteration (i++, shorthand for "increase i by 1"). Together they define exactly where the loop starts, when it stops, and how it advances.

The loop body runs once per iteration, with i taking a new value each time — first 0, then 1, then 2. The moment the condition i < 3 becomes false (once i reaches 3), the loop exits immediately, without running the body a fourth time.