======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 [[PTPScript:Types:Boolean|Boolean]] **''true''** (see [[PTPScript:Types:Boolean#Converting to Boolean|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:

<code ptpscript>
{ 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 }
</code>

<output>
All's well - 9 is equal to 9
</output>

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