0.9b (c) 1995 Peter Childs
SELECT tells the interpreter to select one of a number of instructions. It is used only with WHEN, THEN, END, and sometimes, OTHERWISE. The END instruction marks the end of every SELECT group. The SELECT instruction looks like this:
SELECT WHEN expression1 THEN instruction1 WHEN expression2 THEN instruction2 WHEN expression3 THEN instruction3 ... OTHERWISE instruction instruction instruction END
Note: An IF-THEN instruction cannot be used with a SELECT instruction unless it follows a WHEN or OTHERWISE instruction. You can read this format as follows:
o If expression1 is true, instruction1 is run. After this, processing continues with the instruction following the END. The END instruction signals the end of the SELECT instruction. o If expression1 is false, expression2 is tested. Then, if expression2 is true, instruction2 is run and processing continues with the instruction following the END. o If, and only if, all of the specified expressions are false, then processing continues with the instruction following OTHERWISE.
This diagram shows the SELECT instruction:![]()
A DO-END instruction could be included inside a SELECT instruction as follows:
SELECT WHEN expression1 THEN DO instruction1 instruction2 instruction3 END . . .
You can use the SELECT instruction when you are looking at one variable that can have several different values associated with it. With each different value, you can set a different condition.
For example, suppose you wanted a reminder of weekday activities. For the variable day, you can have a value of Monday through Friday. Depending on the day of the week (the value of the variable), you can list a different activity (instruction). You could use a procedure such as the following, SELECT.CMD, which chooses from several instructions.
Note: A THEN or ELSE instruction must be followed by an instruction.
/* Selecting weekday activities */ SAY 'What day is it today?' Pull day SELECT WHEN day = 'MONDAY' THEN SAY 'Model A board meeting' WHEN day = 'TUESDAY' THEN SAY "My Team Meeting" WHEN day = 'WEDNESDAY' THEN NOP /* Nothing happens here */ WHEN day = 'THURSDAY' THEN SAY "My Seminar" WHEN day = 'FRIDAY' THEN SAY "My Book Review" OTHERWISE SAY "It is the weekend, anything can happen!" END EXIT
NOP Instruction: If you want nothing to happen for one expression, use the NOP (No Operation) instruction, as shown in the previous example for Wednesday.
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