Case

Case is used to provide an alternative control structure based on the value of a given expression.

Syntax

 Case EXPRESSION
    When EXPRESSION_LIST
      INSTRUCTIONS
    ...
    When Default
      INSTRUCTIONS
 Endcase

* `EXPRESSION_LIST` is a list of expressions (at least one) separated by commas. * `EXPRESSION` is an expression that is evaluated and compared to the values found by calculating successively the expressions in EXPRESSION_LIST for the following `When EXPRESSION_LIST` instructions. The instructions found after the first matching `When` instruction are executed, and then the execution resumes after the `Endcase` instruction.

The When Default is optional; if present, it must be the last When instruction of the Case. The instructions placed after it will be executed only if no matching expression was found in all the When instruction following the Case.

Examples

 # Depending on the value of CHOICE, a particular action will be performed.
 # If "R" is chosen, nothing is done.
    Case toupper(CHOICE)
           When "E","D" :  Gosub DELETION
           When "Q","S" :  Goto QUIT
           When "R"
           When "M"     :  Gosub MODIFICATION
           When Default : Gosub HELP
    Endcase
   # Alternative on the expression date$-NUMBER_OF_DAYS that is compared to
   # other variables or complex expressions
   # For all the other cases, as there is no "When Default" instruction, nothing will be executed
   #
    Case date$-NUMBER_OF_DAYS
           When [29/05/1959]
                   RESULT="This is my birthday"
           When [18/06/1944],[08/05/1945],[11/11/1918]
                   RESULT= "This was a historical date"
                   RESULT+=" ("+format$(D:DD[/]MM[ ]4Y",date$-NUMBER_OF_DAYS)+")"
           When date$
                   RESULT "We are today"
                   Gosub ACTIONS_TODAY
    Endcase

Description and comments

• Case is used to allow alternatives within a script based on the value of an expression that will be compared to lists of values.
• At most, one alternative is executed (a Case is the same as [If] … [Elsif] … [Else] … [Endif]). If there is no When Default instruction and if no value matches the expression, no instruction in the Case will be executed.
• No instruction can be placed within the Case and the first When (not even a comment).
• When no instructions are found between a When and the next Wheninstruction, no instruction will be executed if the first When matches the Case, unlike languages such as C. In order to execute the same instructions for several values, you have to put them in a list that follows the When instruction.

Errors

Code	Description
10	An expression found in a list cannot be compared to the expression following the Case (the data types are not compatible).

See also

When, Endcase, If, Then, Else, Endif.