CASE
The CASE
instruction specifies statement
blocks that must be executed conditionally.
Syntax 1
CASE expression-1
WHEN expression-2
{
statement |
EXIT CASE }
[...]
[
OTHERWISE
{
statement |
EXIT CASE }
[...]
]
END CASE
- expression-1 is any expression supported by the language.
- expression-2 is an expression that is tested against expression-1.
- expression-1 and expression-2 should have the same data type.
- statement is any instruction supported by the language.
Syntax 2
CASE
WHEN boolean-expression
{
statement |
EXIT CASE }
[...]
[
OTHERWISE
{
statement |
EXIT CASE }
[...]
]
END CASE
- boolean-expression is any boolean expression supported by the language.
- statement is any instruction supported by the language.
Usage
In a CASE
flow
control block, the first matching WHEN
block is
executed. If there is no matching WHEN
block,
then the OTHERWISE
block is executed. If
there is no matching WHEN
block and no OTHERWISE
block,
the program execution continues with the next statement following
the END CASE
keyword.
The EXIT
CASE
statement transfers the program control to the statement
following the END CASE
keyword. There is
an implicit EXIT CASE
statement at the
end of each WHEN
block and at the end of
the OTHERWISE
block. The OTHERWISE
block
must be the last block of the CASE
instruction.
A null expression is considered as false: When doing a CASE expr
... WHEN [NOT] NULL
using the syntax
1, it always evaluates to FALSE
. Use syntax
2 as CASE ... WHEN expr IS NULL
to
test if an expression is null.
Make sure that expression-2 is not a boolean expression when using the first syntax. The compiler will not raise an error in this case, but you might get unexpected results at runtime.
If there is more than one expression-2 matching
expression-1 (syntax 1), or if two boolean
expressions (syntax 2) are true, only the first matching WHEN
block
will be executed.
Example
MAIN
DEFINE v CHAR(10)
LET v = "C1"
-- CASE Syntax 1
CASE v
WHEN "C1"
DISPLAY "Value is C1"
WHEN "C2"
DISPLAY "Value is C2"
WHEN "C3"
DISPLAY "Value is C3"
OTHERWISE
DISPLAY "Unexpected value"
END CASE
-- CASE Syntax 2
CASE
WHEN ( v="C1" OR v="C2" )
DISPLAY "Value is either C1 or C2"
WHEN ( v="C3" OR v="C4" )
DISPLAY "Value is either C3 or C4"
OTHERWISE
DISPLAY "Unexpected value"
END CASE
END MAIN