======Boolean======

A Boolean expresses a "truth" value, and can therefore be **''true''** or **''false''**. **''true''** and **''false''** are [[PTPScript:Constants|Constants]], so can be used in expressions.

For example:

<code ptpscript>
{ a = true }
{ b = false }

{ if a }
...
{ endif }

{ if a == true }
...
{ endif }

{ if a === true }
...
{ endif }
</code>

Note that in the example above, each ''If'' statement checks for the "truthfulness" of variable ''a'', but the final statement (''if a === **true**'') also checks that ''a'' is explicitly boolean. That is because non-explicit statements perform a conversion to Boolean before making the comparison.

====Converting to Boolean====

To explicitly convert a value to Boolean, the [[PTPScript:Operators:Type Casting|Boolean typecast operator]] - ''?'' - should be used. Some operators, such as the boolean logic NOT operator - ''!'' or ''not'' - also explictly convert a value to Boolean.

When converting to Boolean, the following values are considered to be **''false''**:

  * A Boolean with value **''false''**
  * A [[Number|Number]] with value zero (''0'' or ''0.0'')
  * An empty [[String|String]] - ''""''
  * A String containing a single zero - ''"0"''
  * An empty [[Array|Array]] (with no elements)

Every other value is considered to be **''true''**.

<note warning>
The number ''-1'' is considered to be **''true''**, just like any other non-zero number.
</note>