SELECT, END, WHEN, OTHERWISE, and NOP Instructions

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

┴╓: 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.

┴╓: 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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