Branching
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Use branching statements to restrict the execution of a code block until a particular condition is satisfied.
If...Then...Else
The most common branching statement is the If statement as shown in the following example:
IfA>3Then B=2 EndIf
The B = 2 assignment only occurs when value of variable A is greater than three. A variation of the If statement is the If/Else clause:
IfA>3Then B=2 Else B=0 EndIf
In this example, the variable B is assigned the value of 2 when A is greater than 3, otherwise B is assigned the value of 0.
For more complex statements, you can cascade the If statement, for example:
IfA=0Then B=0 ElseIfA<3Then B=1 Else B=2 EndIf
If the value of variable A equals zero, B is assigned the value 0. If A is less than 3 (but not equal to zero), then B is assigned the value 1. In all other instances (that is, if A is greater than or equal to 3), B is assigned the value 2.
A complete If statement may be written on a single line, with a simpler syntax. The first example of this page may be written as:
IfA>3ThenB=2
The second example of this page may be written as:
IfA>3ThenB=2ElseB=0
Select...Case
The Select...Case instruction is an alternative to the cascaded If statement and is used when you need to check a value against various conditions:
SelectCaseDayOfWeek Case1: NameOfWeekday="Sunday" Case2: NameOfWeekday="Monday" Case3: NameOfWeekday="Tuesday" Case4: NameOfWeekday="Wednesday" Case5: NameOfWeekday="Thursday" Case6: NameOfWeekday="Friday" Case7: NameOfWeekday="Saturday" EndSelect
In this example, the name of a weekday corresponds to a number, so that the DayOfWeek variable is assigned the value of 1 for Sunday, 2 for Monday value, and so on.
The Select command is not restricted to simple 1:1 assignments — you can also specify comparison operators or lists of expressions in a Case branch. The following example lists the most important syntax variants:
SelectCaseVar Case1To5 ' ... Var is between the numbers 1 and 5 (including the values 1 and 5). Case>100 ' ... Var is greater than 100 Case6,7,8 ' ... Var is 6, 7 or 8 Case6,7,8,>15,<0 ' ... Var is 6, 7, 8, greater than 15, or less than 0 CaseElse ' ... all other instances EndSelect
Now consider a misleading (advanced) example, and a common error:
SelectCaseVar CaseVar=8 ' ... Var is 0 CaseElse ' ... all other instances EndSelect
The statement (Var = 8) evaluates to TRUE if Var is 8, and FALSE otherwise. TRUE is -1 and FALSE is 0. The Select Case statement evaluates the expression, which is TRUE or FALSE, and then compares that value to Var. When Var is 0, there is a match. If you understand the last example, then you also know why this example does not do what it appears
SelectCaseVar CaseVar>8AndVar<11 ' ... Var is 0 CaseElse ' ... all other instances EndSelect