7.35: A class cannot redefine a name used earlier outside the class as a type definition.

[xjay73]

Line 9 is an error, redefining a name that had been used as a type earlier outside the class scope -- note that some compilers will not flag this as an error.

In lines 10, 11, and 16, then, Type will be std::string.
Line 18, then, has a type-mismatch error, since parm is a std::string (no conversion from std::string to int.)
Line 19, then, returns the wrong type.

To correct the errors, use a different name than Type for the in-class type definition of double, and adjust the name in lines 10, 11, and 16. Adjusting all three will fix the errors in lines 18 and 19 without further changes.