Learn to Program with Small Basic

Listing 9-4 shows an example of using the Or operator. The goal is to
end the game if there’s no more time to play (timeLeft = 0) or if the player
has lost all their energy (energyLevel = 0).
1 ' OrDemo.sb
2 TextWindow.Write("Time left: ")
3 timeLeft = TextWindow.ReadNumber()
4
5 TextWindow.Write("Energy level: ")
6 energyLevel = TextWindow.ReadNumber()
7
8 If ((timeLeft = 0) Or (energyLevel = 0)) Then
9 TextWindow.WriteLine("Game Over!")
10 EndIf
Listing 9-4: The Or operator
If timeLeft is 0 or energyLevel is 0, Small Basic runs the command inside
the If block (line 9). Run this program several times using different inputs
to make sure you understand how the Or operator works.
You could use nested If statements to do the same thing. For example,
you could replace lines 8–10 with the following code:
If (timeLeft = 0) Then
TextWindow.WriteLine("Game Over!")
Else
If (energyLevel = 0) Then
TextWindow.WriteLine("Game Over!")
EndIf
EndIf
However, as you can see, using nested If statements takes up seven lines
of code, but using Or took only three! Using the Or operator is a more concise
way to test multiple conditions.
The Cosmic Order of Evaluation
Look at the following condition. How does Small Basic evaluate this
expression?
If (A = 1 Or B = 1 And C = 1) Then
As it turns out, Small Basic gives And a higher priority than Or. This
means it finds B = 1 And C = 1 first, and then the result is used as the right
operand for the Or expression. To change the order, you can use parentheses,
like this:
If ((A = 1 Or B = 1) And C = 1) Then
Using Decisions to Make Games 119