Learn to Program with Small Basic

Animated Squares
Let’s write a program that creates a 4×8 grid of randomly colored squares
and then animates these squares to fly to the upper-left corner of the
graphics window, as shown in Figure 17-4.
Before animation
During animation
Figure 17-4: Illustrating the output of AnimatedSquares.sb
The complete application is shown in Listing 17-2.
1 ' AnimatedSquares.sb
2 ' Creates a 4x8 grid of randomly colored squares
3 For r = 1 To 4 ' 4 rows
4 For c = 1 To 8 ' 8 columns
5 clr = GraphicsWindow.GetRandomColor()
6 GraphicsWindow.BrushColor = clr
7 box[r][c] = Shapes.AddRectangle(20, 20) ' Adds a square
8 Shapes.Move(box[r][c], c * 20, r * 20) ' Positions it
9 EndFor
10 EndFor
11
12 ' Animates the squares to the upper-left corner of the window
13 For r = 1 To 4
14 For c = 1 To 8
15 Shapes.Animate(box[r][c], 0, 0, 1000)
16 Program.Delay(400) ' A small delay (in milliseconds)
17 EndFor
18 EndFor
Listing 17-2: Using a matrix to store shape IDs
The program uses a nested For loop to create the squares (lines 3–10).
The outer loop (which creates the rows) runs four times, and the inner
loop (which creates the columns) runs eight times (lines 3–4), for a total of
32 iterations (4×8). In each pass of the inner loop, the square’s color is set
by changing the BrushColor property (lines 5–6), and a square is created by
calling AddRectangle(). We save its identifier in box[r][c] (line 7) and then
move the created square to its position on the square grid (see Figure 17-4).
Let’s take a closer look at lines 7–8.
At line 7, the AddRectangle() method takes the width and the height of
the desired rectangle and returns an identifier of the created shape. In this
example, we pass 20 for both arguments to create a square, and we save
the returned identifier in box[r][c].
Expanding to Higher-Dimension Arrays 245