4.3) Conditional Blocks
If in the previous example we want statement 1 and/or statement 2 to consist of more than one statement, then we need to use a BEGIN and ENDIF:
IF condition THEN BEGIN statement 1a statement 1b statement 1c ENDIF
The statements between a BEGIN and an END are called a block of statements. These can only be used within programs/functions/procedures and not at the IDL command line.
IF condition THEN BEGIN statement 1a statement 1b statement 1c ENDIF ELSE BEGIN statement 2a statement 2b statement 2c ENDELSE