Why do parameters have names in the function declaration?

Question

So my prof has a sample .h file with the following operators at the end

//ComplexNumber.h #include <iostream> using namespace std; #ifndef MY_COMPLEX_H #define MY_COMPLEX_H class complexNumber { public: complexNumber(); complexNumber(double a, double b); void setReal(double a); void setImaginary(double b); double getReal(); double getImaginary(); void printComplex(); private: double realPart; double imaginaryPart; }; complexNumber add(complexNumber A, complexNumber B); complexNumber subtract(complexNumber A, complexNumber B); complexNumber multiply(complexNumber A, complexNumber B); complexNumber divide(complexNumber A, complexNumber B); complexNumber operator +(complexNumber A, complexNumber B); complexNumber operator -(complexNumber A, complexNumber B); complexNumber operator *(complexNumber A, complexNumber B); complexNumber operator /(complexNumber A, complexNumber B); ostream & operator << (ostream &outs, complexNumber A); // istream & operator >> (istream &ins, complexNumber &A); #endif

where is he getting complexNumber A and complexNumber B? I don't see these as variables anywhere...

ah seems those are functions which he expands on in the .cpp file — Zach Smith
– Zach Smith, Commented Sep 14, 2010 at 0:45
Note also that (a) it's a bad idea for a wide variety of reasons to use a using directive (e.g. using namespace std;) in a header file (or, in my opinion, any source file) and (b) usually you would implement such functions and operators as taking parameters of type const complexNumber& (though that depends; I wouldn't necessarily balk at using pass-by-value for a class this small). — James McNellis
– James McNellis, Commented Sep 14, 2010 at 1:22

James McNellis · Accepted Answer · 2010-09-14 00:44:02Z

4

A and B are function parameters of type complexNumber. In a declaration that is not a definition, the names A and B don't mean anything; the following two are the same:

complexNumber add(complexNumber A, complexNumber B); complexNumber add(complexNumber , complexNumber );

It's a good idea to name the parameters, though, because it usually makes function declarations easier to understand and helps make the code self-documenting.

In the definition, if you want to use the argument passed for a given parameter, the parameter has to have a name, otherwise there's no way to identify it.

answered Sep 14, 2010 at 0:44

James McNellis

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12 Comments

Zach Smith Over a year ago

so in the .cpp file i would then build on those definitions from the .h file?

James McNellis Over a year ago

@HollerTrain: Yes. You would define those functions in a .cpp file. Make sure you have a good introductory C++ book; such a book will help you to understand the language.

T.T.T. Over a year ago

are these considered prototypes? why aren't they part of the class?

dash-tom-bang Over a year ago

@Tommy - they are prototypes and they don't need to be part of the class to function. Typically, implementing free functions is preferable to implementing class members, if those functions can do everything that they need to do through the class's public interface. (Oftentimes I see A and B called lhs and rhs, for left- and right-hand side.)

Zach Smith Over a year ago

so it can be same as complexNummber operator +(complexNumber A, complexNumber B);

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