Release 10.1A: OpenEdge Development:
Progress 4GL Handbook

The CASE statement

If you have a sequence of IF,THEN,ELSE clauses that all operate on different values of the same variable or expression, you can combine these into a single block using the CASE statement, which has this syntax:

CASE expression :   { WHEN value [ OR WHEN value ] ... THEN        { block | statement }   } ...   [ OTHERWISE        { block |statement }   ] END [ CASE ].

The expression can be a simple field or variable or any other expression involving multiple fields or values. Part of the optimization of the CASE statement is that it evaluates the expression only once, when the CASE statement is entered. By contrast, nested IF statements evaluate the expression in each IF clause, even if the expression is the same each time.

Following the block header are a number of WHEN clauses, each of which starts with a value for the expression, followed by THEN, followed by a statement or block to execute if the expression has that value. You can combine multiple WHEN clauses with OR if the same block or statement executes on multiple values of the expression.

Finally, the CASE block can conclude with an optional OTHERWISE clause with a statement or block to execute if the expression matches none of the values in the WHEN clauses.

The CASE statement is most useful when a variable or field can have one of a small number of possible values, and the procedure needs to react differently to each value.

Here’s a simple example that uses the CASE statement to count the number of Orders of different types. There are four valid values for the OrderStatus field. The OTHERWISE clause tallies any that don’t match any of the valid values (as it turns out, there aren’t any):

DEFINE VARIABLE iOrderStatus AS INTEGER EXTENT 5     NO-UNDO.   FOR EACH Order:     CASE Order.OrderStatus:         WHEN "Shipped" THEN             iOrderStatus[1] = iOrderStatus[1] + 1.         WHEN "Ordered" THEN             iOrderStatus[2] = iOrderStatus[2] + 1.         WHEN "Back Ordered" THEN             iOrderStatus[3] = iOrderStatus[3] + 1.         WHEN "Partially Shipped" THEN             iOrderStatus[4] = iOrderStatus[4] + 1.         OTHERWISE             iOrderStatus[5] = iOrderStatus[5] + 1.     END CASE.   END.  /* END FOR EACH Order */   DISPLAY iOrderStatus[1] LABEL "Shipped Orders" SKIP           iOrderStatus[2] LABEL "Ordered Orders" SKIP           iOrderStatus[3] LABEL "Back Ordered Orders" SKIP           iOrderStatus[4] LABEL "Partially Shipped Orders" SKIP           iOrderStatus[5] LABEL "Invalid Orders"      WITH FRAME DisplayFrame SIDE-LABELS.

Figure 21–1 shows the result.

Figure 21–1: Result of CASE statement example