Boolean Type

A Boolean value can be either true or false. The name "boolean" comes from George Boole, a 19th century mathematician who invented the algebraic system for these true and false values.

Boolean values are used to make decisions. For instance, an if statement uses a boolean value to decide whether to run one block of statements or another. A while statement uses a boolean value at the end of each loop to decide whether to loop again.

The values true and false can be used directly, as in the following example.

dim x as Boolean

x = true

x = false

The not operator will change a true value to false, or a false value to true.

dim x = not false ' x is true

dim y = not x ' y is false

The and operator forms a new boolean value by comparing two input boolean values. The result is true only if both of the inputs are true.

dim a = true

dim b = false

dim c = true

dim d = a and b ' d is false

dim e = a and c ' e is true

The or operator works like the and operator, but the result is true if either (or both) of the inputs are true.

dim a = true

dim b = false

dim c = false

dim d = a or b ' d is true

dim e = b or c ' e is false

It is often useful to write a function that inspects its parameters and returns a boolean based on some criteria. In the following example, the IsMedicalProfession function returns true if the input is "doctor" or "nurse", but false for "programmer".

function IsMedicalProfession(profession as String) as Boolean

return profession = "doctor" or profession = "nurse"

end function