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ZBasic Language Reference
33
ZX Microcontroller Family
2.5.10 If-Then-Else Statement
The if-then-else compound statement is the basic decision making construct in ZBasic. In its simplest
form, the syntax is:
If <boolean-expression> Then
<statements>
End If
The <boolean-expression> element is an expression whose value is of type Boolean. It most often
involves one of the conditional operators that allow you to compare the values of two expressions but it
may also simply be the invocation of a function whose return type is Boolean.
The <statements> element represents zero or more ZBasic statements possibly including other If
statements. This allows you to create nested decision-making statements of arbitrary complexity.
Although the construction described above is useful, it is often the case that you want your program to
execute a certain set of statements if a condition is true but you want it to execute a different set of
statements if the condition is false. The If statement allows this logic using the syntax shown below.
If <boolean-expression> Then
<statements>
Else
<statements>
End If
Sometimes you’ll want to test several different conditions and execute a different set of statements in
each case. The If statement allows this logic using the following syntax:
If <boolean-expression> Then
<statements>
ElseIf <boolean-expression> Then
<statements>
Else
<statements>
End If
The ElseIf portion of the statement, including the associated statements, may occur zero or more
times. The Else portion of the statement, along with its associated statements, may occur zero or one
times. Note that the logic of the If-Then-Else statement is designed so that at most one set of statements
gets executed. This construct represents a series of tests that are performed sequentially. The first such
test that produces a Boolean True result will cause the statements associated with that test to be
executed. If none of the tests produce a True result and an Else clause exists, the statements
associated with the Else will be executed. In all cases, after the set of statements is executed, control
transfers to the first statement following the End If.
If the same expression is being repeatedly tested against different values, it is more efficient to use the
Select-Case statement described in Section 2.5.11.
Examples
If (i > 3) Then
Call PutPin(12, zxOutputLow)
Else
j = 55
Call PutPin(12, zxOutputHigh)
End If
If i > 3 Then
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