Basic programming with blocks

In block programming (tools like Scratch), you drag coloured blocks together like puzzle pieces. Each block is a command: move 10 steps, show text, wait 1 second.

Blocks only fit together in ways that work — so you cannot make a syntax error. You can build:

• a sequence: blocks one after another,
• a loop: repeat 10 times around other blocks,
• a condition: if on edge then bounce.

Read the program before you run it:

when green flag clicked
repeat 4 times
    move 50 steps
    turn 90 degrees
show text «Done!»

What does the sprite draw? A square (four sides, four corners). What happens if you change 4 to 3 and 90 to 120? A triangle!

Build it in Scratch (scratch.mit.edu, free) and turn on the pen so you can see the trail.