progress-4gl Conditional statements IF ... THEN ... ELSE-statement

Example

In the IF THEN ELSE statement the result can be either a single statement:

DEFINE VARIABLE i AS INTEGER     NO-UNDO.

IF i = 0 THEN
    MESSAGE "Zero".
ELSE 
    MESSAGE "Something else".

Or a block, for instance by adding a DO-block:

DEFINE VARIABLE i AS INTEGER     NO-UNDO.

IF i = 0 THEN DO:
    RUN procedure1.
    RUN procedure2.
END.
ELSE DO: 
    RUN procedure3.
    RUN procedure4.
END.

Several IF-statements can be nested with the ELSE IF-syntax:

DEFINE VARIABLE i AS INTEGER     NO-UNDO.

IF i = 0 THEN DO:
    RUN procedure1.
    RUN procedure2.
END.
ELSE IF i = 1 THEN DO:
    RUN procedure3.
    RUN procedure4.

END.
ELSE DO: 
    RUN procedure5.
    RUN procedure6.
END.

The ELSE-part is not mandatory:

DEFINE VARIABLE l AS LOGICAL     NO-UNDO.

l = TRUE.

IF l = TRUE THEN DO:
    MESSAGE "The l variable has the value TRUE" VIEW-AS ALERT-BOX.
END.

The IF/ELSE IF can compare several conditionals, with or without internal connections. This leaves you free to mess up your code in several ways:

DEFINE VARIABLE i AS INTEGER     NO-UNDO.
DEFINE VARIABLE l AS LOGICAL     NO-UNDO.

IF i < 30 OR l = TRUE THEN DO:
    
END.
ELSE IF i > 30 AND l = FALSE OR TODAY = DATE("2017-08-20") THEN DO:

END.
ELSE DO:
    MESSAGE "I dont really know what happened here".
END.