Visual programming with Scratch

4.1 Getting started with Scratch

Scratch is a block-based programming language. Drag colour-coded blocks together to build scripts.

• Stage: where the action happens.
• Sprite: a character or object on the stage.
• Backdrop: the stage's background.
• Scripts: the code that runs for a sprite.

Block categories (colours)

4.2 Sprites, costumes & naming

• Each sprite can have several costumes (different appearances). Switching costumes makes it look animated.
• Name your sprites sensibly (e.g. "ball", "player1") — it makes scripts much easier to read.

4.3 Duplicating sprites & backdrops

• Right-click → Duplicate makes an exact copy with all its scripts. Useful for enemies, projectiles, etc.
• Add a backdrop from the library or paint your own.

4.4 Interacting with keypresses and other sprites

Common event blocks:

• When green flag clicked — run when the project starts.
• When [space] key pressed — run when a key is pressed.
• When this sprite clicked.
• When I receive [message] — broadcast/receive lets sprites talk to each other.

Detecting collisions: if <touching [other sprite]?> then ….

4.5 Variables

A variable stores a value (number or text) you can use later. In a game it's how you keep score, lives, level.

• Set variable to a value (e.g. set score to 0).
• Change variable by an amount (e.g. change score by 1).
• Show / hide on the stage.

Use if … then … else to react to variable values:

if <lives = 0> then
    say "Game over"
    stop all

4.6 Timers

• The built-in timer starts at 0 and counts up in seconds. Reset with the "reset timer" block.
• Combine with the wait block to space things out, or with repeat until to make a count-down loop.
• Use a variable like time_left if you want a count-down displayed.