Does the OPER contain a double-precision floating point number?
[C++]
BOOL IsDouble() const;
Returns TRUE if the COper contains a single floating point value, FALSE otherwise.
Header: xllplus.h
COper Class 
					  | COper Methods			 
					  | COper::IsArray()			 
					  | COper::IsError()			 
					  | COper::IsBool()			 
					  | COper::IsString()			 
					  | COper::IsEmpty()			 
					  | COper::IsMissing()			 
					  | COper::IsPresent()