If Command

The If command is a core logic construct in any language. It allows for conditional evaluation and output.

There are four commands that belong to the If family - If, ElseIf, Else, and EndIf. Each If command has to have a corresponding EndIf command, and in between there can be any number of ElseIf commands, and optionally one Else command as well.

The If and ElseIf commands consist of the command followed by an expression. The Else and EndIf commands do not use expressions, and so will ignore any expression given. If the result of the expression evaluation equates to Boolean true (see Converting to Boolean), then the information contained after the command, and before the next command in the same control structure, is evaluated by the PTP engine. Otherwise, the next command in the structure is checked. Once one of the expressions has equated to true, none of the other command expressions in the structure are evaluated. If an Else is present, it will be deemed true if the initial If statement, and none of the preceding ElseIf statements, have equated to false.

For example:

{ if 5 == 6 }…
Well, that's weird! 5 is equal to 6!
{ elseif 9 == 9 }…
All's well - 9 is equal to 9
{ else }…
Something seems to have gone wrong...
{ endif }

All's well - 9 is equal to 9

If structures can be nested indefinitely within other If structures, and within other command structures.

ptpscript/commands/if.txt · Last modified: 2007/01/24 10:15
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