CASE statement

Syntax

BEGIN CASE
   CASE expression      statements   [ CASE expression      statements         .
         .
         .                ]
END CASE

Description

Use the CASE statement to alter the sequence of instruction execution based on the value of one or more expressions. If expression in the first CASE statement is true, the following statements up to the next CASE statement are executed. Execution continues with the statement following the END CASE statement.

If the expression in a CASE statement is false, execution continues by testing the expression in the next CASE statement. If it is true, the statements following the CASE statement up to the next CASE or END CASE statement are executed. Execution continues with the statement following the END CASE statement.

If more than one CASE statement contains a true expression, only the statements following the first such CASE statement are executed. If no CASE statements are true, none of the statements between the BEGIN CASE and END CASE statements are executed.

If an expression evaluates to the null value, the CASE statement is considered false.

Use the ISNULL function with the CASE statement when you want to test whether the value of a variable is the null value. This is the only way to test for the null value since null cannot be equal to any value, including itself. The syntax is:

CASE ISNULL (expression)

Use an expression of the constant "1" to specify a default CASE to be executed if none of the other CASE expressions evaluate to true.

Examples

In the following example NUMBER is equal to 3. CASE 1 is always true, therefore control is transferred to subroutine 30. Once the subroutine RETURN is executed, control proceeds to the statement following the END CASE statement.

NUMBER=3
BEGIN CASE
   CASE NUMBER=1
      GOTO 10
   CASE 1
      GOSUB 30
   CASE NUMBER<3
      GOSUB 20
END CASE
PRINT 'STATEMENT FOLLOWING END CASE'
GOTO 50
10*
PRINT 'LABEL 10'
STOP
20*
PRINT 'LABEL 20'
RETURN
30*
PRINT 'LABEL 30'
RETURN
50*

This is the program output:

LABEL 30
STATEMENT FOLLOWING END CASE

In the following example, control proceeds to the statement following the END CASE because 'NAME' does not meet any of the conditions:

NAME="MICHAEL"
BEGIN CASE
   CASE NAME[1,2]='DA'
      PRINT NAME
      GOTO 10
   CASE NAME[1,2]='RI'
      PRINT NAME
      GOSUB 20
   CASE NAME[1,2]='BA'
      PRINT NAME
      GOSUB 30
END CASE
PRINT 'NO MATCH'
STOP

This is the program output:

NO MATCH