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Block-based programming
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Block-based languages such as Scratch let you build programs by snapping blocks together. You cannot make spelling mistakes, so you can focus on the logic.
Events and sequence
A Scratch script starts with an event block, such as when green flag clicked or when this sprite clicked.
The blocks underneath run in order, top to bottom: that is sequence.
Motion blocks move a sprite: move (10) steps, turn (15) degrees.
The blocks underneath run in order, top to bottom: that is sequence.
Motion blocks move a sprite: move (10) steps, turn (15) degrees.
Loops
repeat (10) runs the blocks inside it 10 times.
forever runs them again and again until the program is stopped.
To draw a square with the pen: repeat (4) { move (100) steps, turn (90) degrees }.
For any regular shape, the turn is 360 ÷ number of sides.
forever runs them again and again until the program is stopped.
To draw a square with the pen: repeat (4) { move (100) steps, turn (90) degrees }.
For any regular shape, the turn is 360 ÷ number of sides.
Decisions and variables
if < > then runs blocks only when a condition is true, for example: if touching edge then say Ouch!
Variables store data, such as a score. Blocks like change [score] by (1) update them.
ask [What is your name?] and wait gets input; the reply is stored in answer.
Variables store data, such as a score. Blocks like change [score] by (1) update them.
ask [What is your name?] and wait gets input; the reply is stored in answer.
A sprite should draw a regular pentagon (5 sides). What should go inside the repeat loop?
- A pentagon has 5 sides, so repeat (5).
- Turn = 360 ÷ 5 = 72 degrees.
Answer: repeat (5) { move (100) steps, turn (72) degrees }
Scripts start with an event block. Blocks run in sequence; repeat and forever loop; if blocks make decisions. For a regular shape, turn 360 ÷ sides degrees.
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