Page 125 - Learn To Program With Scratch

After executing any of the scripts in Figure 5-12, sum will contain
the number 5, making these scripts functionally equivalent. Note that the
method used in the second script is a common programming practice, and
I recommend that you study it for a moment to become comfortable with it.
Now let’s see the change command in action.

Spider Web

SpiderWeb .sb2 We can create a spider web by drawing several hexagons of increasing size,
as shown in Figure 5-13. The Triangle procedure draws an equilateral
tri angle with a variable side length, while the Hexagon procedure calls
Triangle six times with a 60° (that is, 360° / 6) right turn after each call.
The figure clearly shows how the hexagon is made up of the six triangles.

sideLength

Figure 5-13: Creating a spider web by drawing several hexagons of increasing size

The SpiderWeb procedure simply calls Hexagon repeatedly with a dif-
ferent value of the sideLength variable each time. This results in the concen-
tric (that is, having the same center) hexagons you see in the figure. Note
how the change command is used to set the value of sideLength inside the
repeat loop. Reproduce the SpiderWeb procedure, run it, and see how it
works.

Pinwheel
Pinwheel .sb2 This example is similar to the previous one except that this time, we’ll use
a variable to control the number of triangular repetitions. The resulting
procedure (called Pins) is shown in Figure 5-14. The Pinwheel procedure
in the same figure works like the SpiderWeb procedure above, but we also
change the pen’s color each time through the loop for a fun rainbow effect.
Some outputs of the Pinwheel procedure for different pin counts are shown
in the figure. Experiment with this procedure to see what else you can
create.

Variables 103

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