The SWITCH statement is used to select one statement or block of statements for execution from multiple choices, depending upon the value of the expression following the word SWITCH.
Each statement that is part of a SWITCH statement is preceded by an expression that is compared to the value of the SWITCH expression. SWITCH executes by comparing the SWITCH expression with each selector expression in the order written. If a match is found, program execution jumps to that statement and execution continues from that point. Whereas CASE executes at most one statement within the CASE block, SWITCH executes the first matching statement and any following statements in the SWITCH block. Once a match is found in the SWITCH block, execution falls through to any remaining statements. For this reason, the BREAK statement is commonly used within SWITCH statements to force an immediate exit from the SWITCH block.
The ELSE clause of the SWITCH statement is optional. If included, it matches any selector expression, causing its code to be executed. For this reason, it is usually written as the last clause in the switch statement. The ELSE statement is executed only if none of the preceding statement expressions match. If an ELSE clause is not included and none of the values match the selector, program execution continues immediately below the SWITCH without executing any of the SWITCH statements.
For more information on the difference between CASE and SWITCH, see CASE Versus SWITCH.
SWITCH expression OF
expression: statement
...
expression: statement
ELSE: statement
ENDSWITCH
This example illustrates how, unlike CASE, SWITCH executes the first matching statement and any following statements in the SWITCH block:
PRO ex_switch, x
SWITCH x OF
1: PRINT, 'one'
2: PRINT, 'two'
3: PRINT, 'three'
4: BEGIN
PRINT, 'four'
BREAK
END
ELSE: BEGIN
PRINT, 'You entered: ', x
PRINT, 'Please enter a value between 1 and 4'
END
ENDSWITCH
END
ex_switch, 2
IDL Prints:
two
three
four
|
5.4 |
Introduced |
BEGIN...END , BREAK , CASE , CONTINUE , FOR , FOREACH, GOTO , IF...THEN...ELSE , REPEAT...UNTIL , WHILE...DO