Returns the sum of two variants.
HRESULT VarAdd( [in] LPVARIANT pvarLeft, [in] LPVARIANT pvarRight, [out] LPVARIANT pvarResult );
The function returns one of the following:
Both expressions are of the string type
One expression is a string type and the other a character
One expression is numeric and the other is a string
Both expressions are numeric
Either expression is NULL
NULL is returned.
Both expressions are empty
Integer subtype is returned.