Learn to Program with Small Basic

TRY IT OUT 13-5
What does the following program do? Run the program to check your answer.
For N = 1 To 200
GraphicsWindow.PenColor = GraphicsWindow.GetRandomColor()
x2 = Math.GetRandomNumber(300)
y2 = Math.GetRandomNumber(300)
GraphicsWindow.DrawLine(0, 0, x2, y2)
EndFor
Changing the Step Size
The previous section showed you the syntax of the For loop that automatically
increases the loop counter by one after each iteration. But For loops
have a general form that lets you control the Step size of the loop’s control
variable to increase it or decrease it by however much you want. Here’s the
general form of the For loop:
For N = A To B Step C
Statement(s)
EndFor
It works like the simplified loop you saw earlier. But instead of incrementing
the loop counter N by one, you can decide how much to change N.
You do this by setting the amount in the Step size, C, which can be a positive
or negative number or any Small Basic expression. Let’s look at some
examples that show you how to use this general form of the For loop.
Counting Down by Twos
In this example, the program counts from a starting value (10 in this
case) down to 0, subtracting 2 at a time so the program writes the numbers
10, 8, 6, 4, 2, 0 in the text window. Enter and run the program in
Listing 13-5.
1 ' CountDown.sb
2 For N = 10 To 0 Step -2 ' Uses a negative step size
3 TextWindow.WriteLine(N)
4 EndFor
Listing 13-5: Counting down with Step
A negative value was used for the Step size (line 2) to reduce the value
of the loop counter by 2 after each iteration.
Repeating For Loops 187