Learn to Program with Small Basic

To create this program, we’ll use an array named ball to hold the
numbers of the 10 balls (ball[1] = 1, ball[2] = 2, …, ball[10] = 10). Then
the program selects a random number between 1 and 10 to pick a ball. For
example, if it picks number 2, it sets ball[2] = 0 to indicate that the second
ball has been selected and is no longer available. Then it selects another
random number. Let’s say that the second number is also 2. First, the program
checks ball[2]. Because it’s 0, it knows that ball[2] has already been
selected (you can’t take the same ball out of the bag twice!), and it picks
another random number. It continues this until it selects five different
random numbers. The complete program is shown in Listing 15-2.
1 ' RandomSelect.sb
2 For N = 1 To 10 ' Puts the 10 balls in an array
3 ball[N] = N
4 EndFor
5
6 For N = 1 To 5 ' Loops to select 5 balls
7 idx = Math.GetRandomNumber(10) ' Gets random ball number
8 While (ball[idx] = 0) ' Ball already selected
9 idx = Math.GetRandomNumber(10) ' Gets another number
10 EndWhile
11
12 TextWindow.Write(ball[idx] + ", ") ' Displays selected ball
13 ball[idx] = 0 ' Marks it out (taken)
14 EndFor
15 TextWindow.WriteLine("")
Listing 15-2: Randomly selecting five different balls
The program starts by setting ball[1] = 1, ball[2] = 2, . . . , ball[10] = 10
in a For loop (lines 2–4). It then begins a loop to select the five balls (line 6).
In each iteration of the loop, it picks a random number, idx, between 1 and 10
(line 7). A While loop continually sets idx until ball[idx] is not 0 (lines 8–10).
After selecting a unique ball number, the program displays the number
(line 12), and then it marks that ball as selected by setting its array element
to 0 (line 13) so it doesn’t try to select that number again. Here’s a sample
run of this program:
5, 9, 10, 1, 2,
Run the program to see which numbers you get!
A Magic 8 Ball
In this example, we’ll write a program that simulates a Magic 8 Ball game.
A user asks a yes or no question, and the computer answers. Of course, it’s
just for fun, so don’t use it to make important decisions like choosing your
spouse or house! The complete program is shown in Listing 15-3.
1 ' Magic8Ball.sb
2 ans[1] = "It is certain. Like really, really certain."
Grouping Data in One-Dimensional Arrays 217