Page 162 - Learn To Program With Scratch

Scratch Projects
The new commands you’ve learned in this chapter should allow you to cre-
ate a wide range of useful Scratch applications, and hopefully the projects
I present in this section will give you some ideas for your own projects. I
encourage you try out these applications, understand how they work, and
then think of ways to enhance them.

Guess My Coordinates

GuessMy In this section, we’ll develop an interactive game that can be used to test
Coordinates .sb2 anyone’s knowledge of the Cartesian coordinate system. The game contains
a single sprite (called Star) that represents a random point on the Stage
(see Figure 6-16).

Figure 6-16: The Guess My Coordinates interface

Each time you run the game, the sprite moves to a different location
on the Stage and asks the user to guess its x- and y-coordinates. The game
checks the user’s answers and provides an appropriate feedback message.
The main script for the Star sprite is shown in Figure 6-17.
This script uses two variables, X and Y, to hold the random coordinates
of the sprite. I’ll explain how each numbered section from Figure 6-17 works
below.

1. The X variable is assigned a random value from the set {–220, –200,
–180, ... , 220}. This is achieved by first selecting a random inte-
ger between –11 and 11 and multiplying the result by 20. Similarly,
the Y variable is assigned a random value from the set {–160, –140,
–120, ... , 160}. The selected X and Y values ensure that the resulting
point is located on one of the grid intersection points of Figure 6-16.
The sprite is then moved to the location specified by X and Y.

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