Page 165 - Learn To Program With Scratch

Figure 6-20 shows that this game contains five sprites. Three sprites
(named Scalene, Isosceles, and Equilateral) represent the buttons the user
clicks to select an answer, and the invisible Painter sprite draws the triangle
on the Stage.

n o t e I made the Painter sprite invisible by unchecking its Show checkbox in the sprite info
area. If you prefer to control the sprite’s visibility from the script, you can add a hide
block to explicitly hide the sprite when the game starts.

The Tutor sprite is the game’s main driver; it determines the type of tri-
angle to draw for each run and checks the user’s answer. The scripts for the
Tutor sprite are shown in Figure 6-21.

Set triangle’s type
(1 to 3) for this
No answer yet. question.
Show a new
question, wait
for answer, and
then check the
answer.

Set triangle’s
name based
on its type.

Tell Painter
to draw the
triangle.

Figure 6-21: Scripts for the Tutor sprite . The main driver script (top left) calls
NewQuestion (right) and CheckAnswer (bottom left) .

When the green flag icon is clicked to start the game, the main script
enters an infinite loop. On each pass of the loop, the script sets choice to 0
(to indicate that the player hasn’t answered yet), draws a different triangle,
and waits for an answer. The choice variable should change when the user
clicks any of the three answer buttons. When the user clicks a button to
classify the triangle, the script checks the answer and provides appropriate
feedback. Let’s look at each step in more detail.
The NewQuestion procedure starts by randomly setting type—which
determines the type of the triangle to be drawn on the Stage—to 1, 2, or
3. The script then uses two if/else blocks to set the value of the name vari-
able based on the value of type. The name variable serves two purposes:
(1) it specifies which broadcast message to send so the Painter sprite knows
what to draw (note how the broadcast and wait block uses name), and

Making Decisions 143

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