2. Starter Activity: Maze Games
Check out the maze style games:
http://scratch.mit.edu/tagged/shared/maze
A Mazing Game
3. A Mazing Game
In this lesson you will use algorithms to help code
a solution that uses conditional statements to
make a program loop. You will create a maze style
game.
Lesson
Understand the use of an algorithm to develop a
solution to a problem
Translate an algorithm into code
Use conditional statements
Objectives
4. Introduction
You are going to create a simple game where the
player guides an ‘explorer’ character around a
maze using the arrow keys.
The game will end when the explorer rescues its
friend in the middle.
A Mazing Game
5. Watch the video Maze which is in the
programming in scratch folder in Groupwork to
learn how to create the game.
A Mazing Game
6. Task 6: Setting the Scene
Set up the game by importing the stage costume
(Maze) and two sprites – an explorer and a friend
for the explorer to rescue.
N.B The maze is already in the backgrounds folder
Don’t do any more at this point.
A Mazing Game
7. The Importance of Design
Before you make anything – a house, a car or a
computer program – you should start with a
design.
There are two important parts to most programs
– the interface (how it looks) and the code – you
design these separately.
A Mazing Game
8. The easiest way to design the interface is by
sketching it out on paper.
To design the code, the easiest way is to write out a
list of steps you want the code to perform in
English. This is known as an algorithm.
Algorithms let programmers concentrate on what
the code has to do, instead of how to do it on the
computer.
A Mazing Game
9. Designing the Solution
Think about the two main things that you will
need to code:
1. Moving the explorer around the maze
2. Getting the explorer to rescue its friend
The table on the next slide shows an algorithm for
moving the explorer around the maze and the
Scratch code that does the same thing.
A Mazing Game
10. Algorithm for moving explorer Code
when the flag is clicked
repeat forever
if right arrow key is pressed
point right
move 5 steps
if left arrow key is pressed
point left
move 5 steps
if up arrow key is pressed
point up
move 5 steps
if down arrow key is pressed
point down
move 5 steps
if explorer touches the same
colour as the maze wall
11. Task 7: Moving the Explorer
Using a combination of the algorithm and the code,
develop your game so that you are able to move the
explorer around the maze.
Use of the video is forbidden from this point
onwards.
A Mazing Game
12. Algorithm for moving explorer Code
when the flag is clicked
repeat forever
if right arrow key is pressed
point right
move 5 steps
if left arrow key is pressed
point left
move 5 steps
if up arrow key is pressed
point up
move 5 steps
if down arrow key is pressed
point down
move 5 steps
if explorer touches the same
colour as the maze wall
13. Test your game to see if it works
If it doesn’t see if you can identify the problem.
A Mazing Game
14. Task 8: Rescuing the Explorers Friend
From this algorithm, see if you can create the code
for the friend sprite!
A Mazing Game
Algorithm for reaching centre of maze Code for friend sprite
when the flag is clicked
show sprite
repeat forever
if touching explorer sprite
say “Thank you!”
hide sprite
stop all scripts
Code this one
yourself!
15. Test your game to see if it works
If it doesn’t see if you can identify the problem.
A Mazing Game
16. Plenary: Question 1
A programmer creates a
maze game like the one
you’ve just created.
Unfortunately, the
character doesn’t move
as expected.
What mistake has the
programmer made?
A Mazing Game
17. Plenary:
Look at the two
examples of
code.
Do they
perform the
same task?
A Mazing Game
Question 2
18. Plenary: Question 3
The code adjacent controls a sprite
going round a maze. If the sprite
touches the side of the maze (the
colour blue), it returns to its starting
position of -150, 150.
Unfortunately, the sprite sometimes
touches the walls of the maze and
returns to the start when the player
doesn’t expect.
What mistake has the programmer
made?
A Mazing Game
19. Plenary: Question 4
In this example, the sprite is
supposed to return to the centre
of the maze when it touches the
sides (coloured blue); however,
it only does this sometimes.
What mistake has the
programmer made?
A Mazing Game
20. A Mazing Game
Keywords
Understand the use of an algorithm to develop a
solution to a problem
Translate an algorithm into code
Use conditional statements
Objectives
Loop
Sprites
Interface
Code
Indented
Conditional Statements
Collision Detection
Repetition
Notes de l'éditeur
Left and right arrow both point right (90). Left arrow should point left (-90).
Yes. The forever/ if touching colour? stacks are both executed throughout the program, despite being in separate stacks in the right-hand example . This could be a good opportunity to discuss the concepts of parallelism and modularity again: Q: Why might some think the right-hand script is better than the left-hand? A: It separates movement and collisions into two stacks. These are two separate problems which should arguably be solved separately. This will make the code easier to maintain if new features are added to either aspect.
The sprite moves before pointing in the correct direction. This will make it move 5 steps in the previously selected direction, causing it to touch colour blue if it happens to be close.
The touching colour? block is inside the final if statement, meaning it will only ever be executed if the down arrow is pressed.
