Use branching statements to restrict the execution of a code block until a particular condition is satisfied.
The most common branching statement is the If statement as shown in the following example:
If A > 3 Then B = 2 End If
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:
If A > 3 Then B = 2 Else B = 0 End If
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:
If A = 0 Then B = 0 ElseIf A < 3 Then B = 1 Else B = 2 End If
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.
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:
Select Case DayOfWeek Case 1: NameOfWeekday = "Sunday" Case 2: NameOfWeekday = "Monday" Case 3: NameOfWeekday = "Tuesday" Case 4: NameOfWeekday = "Wednesday" Case 5: NameOfWeekday = "Thursday" Case 6: NameOfWeekday = "Friday" Case 7: NameOfWeekday = "Saturday" End Select
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:
Select Case Var Case 1 To 5 ' ... Var is between the numbers 1 and 5 (including the values 1 and 5). Case > 100 ' ... Var is greater than 100 Case 6, 7, 8 ' ... Var is 6, 7 or 8 Case 6, 7, 8, > 15, < 0 ' ... Var is 6, 7, 8, greater than 15, or less than 0 Case Else ' ... all other instances End Select
Now consider a misleading (advanced) example, and a common error:
Select Case Var Case Var = 8 ' ... Var is 0 Case Else ' ... all other instances End Select
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
Select Case Var Case Var > 8 And Var < 11 ' ... Var is 0 Case Else ' ... all other instances End Select
|Content on this page is licensed under the Public Documentation License (PDL).|