Page 262 - Learn To Program With Scratch

second list (named ans) contains the user’s input, and the third list (named
cellYCenter) contains the 11 vertical positions used by the Letter and the YesNo
sprites (so they know where they should stamp their costumes). When the
user clicks the mouse over any of the answer boxes, the Stage sprite detects
the mouse click and asks for an answer. The Stage sprite updates the cor-
responding element of the ans list to match what the user entered and
stamps that letter over the answer box. Open FlowerAnatomy.sb2 to read the
scripts that read and display the user’s answers.
When the user clicks the Check button, the YesNo sprite, which has the
costumes for the check mark and X images, executes the script shown in
Figure 9-37.

Start a loop to compare all
answers.

Get letter of the correct answer.
Get letter of the user’s answer.

If the answer is correct, switch
to the check mark costume.
Otherwise, switch to the X-mark
costume.
Move to the appropriate position
on the Stage, and stamp the
costume.
Point to the next answer.

Figure 9-37: The Check procedure of the YesNo sprite

The script compares the elements of the correctAns and the ans lists one
by one. If the two values are equal, it stamps a check mark to say the user
was correct. Otherwise, it stamps the red X where the user’s answers were
wrong. Either way, Check consults the cellYCenter list to get the correct posi-
tion for stamping the image. See Try It Out 9-11 on the opposite page.

Other Applications
SayThat The extra resources you downloaded from the book’s website (http://
Number .sb2 nostarch.com/learnscratch/) contain three more applications that you can
explore on your own, with full explanations. The first application is a two-
player game about sorting fractions and decimals. Each player gets 5 ran-
dom cards from a deck of 31 cards. Each player is then dealt one card from
the remaining set. You can either discard the new card or drag it over one
of your current five, replacing the old one. Whoever arranges five cards in
ascending order first wins the game.

240 Chapter 9
www.it-ebooks.info