A simple form for the IF construct is:
statement_block 2 ]
The ELSE section is optional. If the logical expression is true, the first block is executed, otherwise the second.
Logical expressions can be stored as mLOGICAL variables.
If the ELSE section consists of one IF construct, then ELSE and IF can be reduced to ELSEIF provided that one of the associated ENDIFs is deleted. Sometimes it is simpler to use a CASE construct.
IF constructs can be named. Optionally, the same name may be used after ELSE and after ELSEIF (expr) THEN.