Conditions, Loops & Events

Once you can list steps in order, programs need three more building blocks: conditions, loops, and events. Conditions ask a yes/no question. Loops repeat steps. Events listen for something to happen. Mix them together and your program can think, repeat, and react.

Condition — Make a Decision

A condition checks if something is true and then chooses what to do. The shape we use to draw it is a diamond, because a diamond has two paths leaving it: Yes and No.

• If hungry, then eat — otherwise wait.
• If it is raining, then take an umbrella.
• If the score is at least 10, then win the game.
• If it is dark, then turn on the light.

Loop — Repeat Steps

A loop tells the computer to do the same thing over and over without you typing it many times. There are loops that count, loops that visit each item in a list, and loops that keep going until something changes.

• Repeat 5 times — count from 1 to 5.
• For each item in a list — visit every name in turn.
• While the battery is low — keep charging.
• Until the door opens — keep knocking.

Event — Listen and React

An event is a moment the program is waiting for. When it happens, the program runs a chunk of code called a handler. Every game and app you use is full of events.

• When a key is pressed — move the player.
• On button click — submit the form.
• When the game starts — show the title.
• On timer tick — update the clock.