[This is preliminary documentation and subject to change.]
The Boolean data type takes on a value of logical TRUE or logical FALSE. This type is accessed programatically using the Automation type VT_BOOL, which takes on values of VARIANT_TRUE (-1) or VARIANT_FALSE (0). Note the difference between the programmatic representations of logical TRUE in C/C++ and Automation types:
While both types are nonzero and therefore not FALSE, they have different representations for TRUE.