Boolean values are the simplest of data values. They have two possible values: true and false. The output format uses two specifiers: both must be given. The first specifier is for true values; the second is for false values. For example, the current C/Base system format for boolean values is:
Equally valid formats are shown below:
In contrast to the formatting of other data types, there are no special characters or key letters for boolean values. This allows any string to be used for true and false values. The table below shows the result of formatting true and false values.
Format True False
yes;no yes no
Yes;No Yes No
yup;nope yup nope
Y;N Y N
maybe;never maybe never
si;no si no
no;yes no yes
Notice the last example. By allowing any format, it is possible to "reverse" the values being displayed. This type of format is not recommended; it will prove very confusing to users.