This tutorial will introduce you to boolean expressions.

What is a Boolean Expression?

A boolean expression is any expression that evaluates to either True or False.

The two most simple boolean expressions are : True and False.

Boolean expressions are used to by conditional statements and loops to make decisions.

For example :

If True Then Print "This boolean expression is true, so If displayed this."

Sync
WaitKey

Variables can also be used :

boolExp = True

If boolExp Then Print "This boolean expression is true, so If displayed this."

Sync
WaitKey

Data Types as Boolean Expressions

Numbers as Boolean Expressions

As boolean expressions, the only number that is false is 0.

Every other number is true.

If 1  Then Print "1 is 'True', so this was displayed."
If 0  Then Print "You'll never see this."
If -1 Then Print "-1 is also 'True'."

Sync
WaitKey

Many functions return either a 1 or 0 and therefore can be said to return boolean expressions.

SetFPS 60

Do
    Cls 0
        Print "SpaceKey() currently returns: " + Str$( SpaceKey() )
        If SpaceKey() Then Print "SpaceKey() returns 1 when the Space Key is down, so it's True."
    Sync
Loop

Strings as Boolean Expressions

Strings as boolean expressions are always False by themselves.

If "string!" Then Print "This string is False."
Print "Using a string by itself is always False "

Sync
WaitKey

Next Steps

• Logical Operators
• Relational Operators