Page 229 - Learn To Program With Scratch

The Digit sprite has 12 costumes (named d1 through d12), as shown
in Figure 8-32 (right). When this sprite receives the NewProblem broadcast,
it stamps costumes representing the numerators and denominators of the
two operands. Figure 8-32 also shows the procedure that does the actual
stamping.

d1 d2
d3 d4

d5 d6
d7 d8
d9 d10
d11 d12

Example:
num1=3, den1=5
num2=7, den2=9

Figure 8-32: The function of the Digit sprite

The procedure uses nested if/else blocks to determine which costume
corresponds to the digit to be stamped. Note how the costume name for
digits 1 through 9 is formed using the join operator. After switching to
the correct costume, the Digit sprite moves to the specified (x,y) position
and stamps the image of the costume at that location.
When the new problem is shown, the user can click the Read button
to enter an answer. The script associated with this button is illustrated
in Figure 8-33. The part of the script that parses the player’s answer into
two tokens (numerator Hide the sprite so that the
and denominator) is simi- question is asked by the Stage
lar to the one presented (instead of the button itself).
in Figure 8-16 for extract-
ing the angle and distance
from answer in the Shoot
game and, therefore, is Extract the numerator and denominator from

answer and assign them to num3 and den3
not shown here. Check the
FractionTutor.sb2 file for the
complete procedure.
Figure 8-33: The script of the Read sprite

String Processing 207

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