1. Introduction to Programming
Scratch
Lesson 1

2. Goals
• What is an algorithm?
• Scratch Interface
• Variables
• Conditional Statements
• Turtle Graphics
• Repetition
2

3. What is an algorithm?
• A step by step process (Algorithm)
– Instructions for making tea (Pseudocode)
If no water in kettle:
Put water in kettle
Turn on kettle
While water not boiling in kettle:
Wait
Put water in cup …
3

4. Scratch user interface
4

5. Scratch stage
5

6. Stage + Sprite
• Exercise:
– Point your mouse to coordinate x=0, y=0
• Exercise:
– Get a new sprite on the screen
6

7. First scratch program
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8. Variables
Add a variable
called “number”
Exercise:
Say a random number
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9. Conditions
Exercise:
– What does
this code do?
– What are the
errors in the
code?
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10. Conditions
Exercise:
– What does
this code do?
– What are the
errors in the
code?
– What if
“number” is
equal to 5?
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11. Motion statements
• Move Right
• Move Left
• Big Steps
• Small Steps
• Move Up
• Move Down
• Exercise:
Double-click on the
blocks to see what
happens
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12. More motion action
• Exercise
– Make the sprite go to x=0, y=0
• Exercise
– Make the sprite move 100 steps and turn 90 degrees
• Exercise
– Make the sprite go in a square pattern
• Exercise
– Make the sprite move when you hit a key
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13. Pen statements
• Pen appears
underneath sprite
• Pen must be set to
“down” before it will
draw
• Exercise:
Draw a line after the
sprite
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14. Iteration
• Repeat statements
• Exercise:
Guess what this
code does
• Test your guess
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15. Loop exercises
• Exercise: Draw this (10 diamonds)
• Exercise: Try to write your programs with as few statements as
possible
15

16. More repeating exercises
• Exercise: Draw this in any colour
• Exercise: Change the colour of each square
• Exercise: Draw a triangle, a pentagon a hexagon
and a circle.
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