ifstatement

Syntax   An ifStatement is:

 if trueFalseExpn then
  statementsAndDeclarations
 { elsif trueFalseExpn then
  statementsAndDeclarations }
 [ else
  statementsAndDeclarations ]
 end if

Description   An if statement is used to choose among a set of statements (and declarations). One set (at most) is chosen and executed and then execution continues just beyond end if.

The expressions (the trueFalseExpressions) following the keyword if and each elsif are checked one after the other until one of them is found to be true, in which case the statements (and declarations) following the corresponding then are executed. If none of these expressions evaluates to true, the statements following else are executed. If no else is present and none of the expressions are true, no statements are executed and execution continues following the end if.

Example   Output a message based on value of mark.

        if mark >= 50 then
            put "You pass"
        else
            put "You fail"
        end if
Example   Output A, B, C, D or F depending on mark.

        if mark >= 80 then
            put "A"
        elsif mark >= 70 then
            put "B"
        elsif mark >= 60 then
            put "C"
        elsif mark >= 50 then
            put "D"
        else
            put "F"
        end if
Example   If x is negative, change its sign.

        if x < 0 then
            x := - x
        end if
Example   If x is less than zero or greater than maxx, put a message.

        if x < 0  or x > maxx then
            put "Out of bounds!"
        end if
Example   If the boolean flag is true and name is “stop”, put a message and return.

        if flag  and name = "stop" then
            put "Exiting routine"
            return
        end if
Details   Several statements and declarations can appear after a particular then.

See also   case statements for another way to select among statements.