Select Case
Conditional statement block
Select Case expression
[ Case expressionlist]
or
Select Case As Const integer_expression
[ Case constant | enumeration ]
Select Case executes specific code depending on the value of an expression. The expression is evaluated once, and compared against each Case, in order, until a matching expression is found. The code inside the matching Case branch is executed, and the program skips down to the end of the Select Case block. Case Else matches any case not already matched, so if there is a Case Else, at least one Case is guaranteed to be executed. If no Cases match, the whole Select Case block will be skipped.
End Select is used to close the Select Case...End Select block.
Note for C users: In FreeBASIC, Select Case works like a switch block where all cases have a break at the end. As there is no fall-through, multiple options must be put in an expression list in a single Case.
Besides integer types, floating point and string expressions are also supported with the first syntax.
Syntax of an expression list:
{ expression | expression To expression | Is relational operator expression }[, ...]
example of expression lists:
If As Const is used, only Integer constants can be evaluated and the expression list supports single constants and enumerations only. "To" ranges are supported, but "Is" relational operators are not.
With As Const, a jump table is created to contain the full range of integer Cases handled. This allows Select Case As Const to be faster than Select Case. However, the size of the range of values is limited, and the largest value in the range may be no higher than the smallest value + 4096.
Syntax
Select Case expression
[ Case expressionlist]
[statements]
[ Case Else ][statements]
End Selector
Select Case As Const integer_expression
[ Case constant | enumeration ]
[ statements ]
[ Case Else ][ statements ]
End SelectDescription
Select Case executes specific code depending on the value of an expression. The expression is evaluated once, and compared against each Case, in order, until a matching expression is found. The code inside the matching Case branch is executed, and the program skips down to the end of the Select Case block. Case Else matches any case not already matched, so if there is a Case Else, at least one Case is guaranteed to be executed. If no Cases match, the whole Select Case block will be skipped.
End Select is used to close the Select Case...End Select block.
Note for C users: In FreeBASIC, Select Case works like a switch block where all cases have a break at the end. As there is no fall-through, multiple options must be put in an expression list in a single Case.
Besides integer types, floating point and string expressions are also supported with the first syntax.
Syntax of an expression list:
{ expression | expression To expression | Is relational operator expression }[, ...]
- expr: evaluates expr, and compares for equality with the original expression. If they are equal, then a match has been found. This could be considered as a shorthand for "Is = expr" (see below).
- expr1 To expr2: evaluates expr1 and checks to see if it is less than or equal to the original expression. If so, it evaluates expr2, and checks to see if it is greater than or equal to the original expression. If so, then a match has been found.
- Is relational_operator expr: evaluates expr, and compares the original operation against it, using the supplied relational_operator (=, >, <, <>, <=, >=). If the comparison is true, then a match has been found.
example of expression lists:
| Case 1 | constant |
| Case 5.4 To 10.1 | range |
| Case Is > 3 | bigger than-smaller than |
| Case 1, 3, 5, 7 to 9 | match against a set of values |
| Case x | value of a variable |
If As Const is used, only Integer constants can be evaluated and the expression list supports single constants and enumerations only. "To" ranges are supported, but "Is" relational operators are not.
With As Const, a jump table is created to contain the full range of integer Cases handled. This allows Select Case As Const to be faster than Select Case. However, the size of the range of values is limited, and the largest value in the range may be no higher than the smallest value + 4096.
Example
Dim choice As Integer
Input "Choose a number between 1 and 10: "; choice
Select Case As Const choice
Case 1
Print "number is 1"
Case 2
Print "number is 2"
Case 3, 4
Print "number is 3 or 4"
Case 5 To 10
Print "number is in the range of 5 to 10"
Case Else
Print "number is outside the 1-10 range"
End Select
Input "Choose a number between 1 and 10: "; choice
Select Case As Const choice
Case 1
Print "number is 1"
Case 2
Print "number is 2"
Case 3, 4
Print "number is 3 or 4"
Case 5 To 10
Print "number is in the range of 5 to 10"
Case Else
Print "number is outside the 1-10 range"
End Select
Differences from QB
- Select Case As Const did not exist in QB
- in an "expr1 TO expr2" case, QB would always evaluate both expressions, even if expr1 was higher than the original expression.
See also
