Page 221 - Learn To Program With Scratch

try it out 8-5
To check your understanding, practice the following binary-to-decimal conver-
sions: (a) 1010100, (b) 1101001, and (c) 1100001 .

The program starts when the green flag icon is clicked. This event is
trapped by the Driver sprite, which executes the script shown and described
in Figure 8-20.
Tell the Bit sprite to get ready.

Ask user to input an 8-bit binary
number.
Save the user’s answer in a variable
named binary.
Tell the Bit sprite to do the conversion.
The Bit sprite saves the answer in the
decimal variable.
Display the result of the conversion.

Figure 8-20: The script for the Driver sprite

This script prepares the Stage and asks the user to input a binary num-
ber so the Bit sprite can begin a new round of conversion. When the Bit sprite
completes its work, the Driver sprite shows the user the decimal value, which
is computed and stored by the Bit sprite in a shared variable named decimal.
The script that the Bit sprite runs in response to the Initialize message is
illustrated in Figure 8-21.

Move to the right side
of the Stage.
Stamp 8 copies of
the Off costume.

60

Figure 8-21: The Initialize script for the Bit sprite

This script draws a bit pattern representing eight zeros on the Stage.
As you’ll see in a moment, wherever a binary 1 appears in the user’s input
string, the script should stamp a costume of digit 1 over the corresponding

String Processing 199

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