C++ FAQ Celebrating Twenty-One Years of the C++ FAQ!!!
(Click here for a personal note from Marshall Cline.)
Section 13:
13.1 What's the deal with operator overloading?
13.2 What are the benefits of operator overloading?
13.3 What are some examples of operator overloading?
13.4 Is operator overloading supposed to make the class' code clearer?
13.5 What operators can/cannot be overloaded?
13.6 Overloading operator== to use string comparison?
13.7 Can I create operator** for to-the-power-of?
13.8 But which operators should I override?
13.9 Guidelines / "rules of thumb" for overloading operators?
13.10 Creating a subscript operator for a Matrix class?
13.11 Should my Matrix interface look like an array-of-array?
13.12 Part two of making my Matrix interface look like an array-of-array?
13.13 Designing classes from the outside-in vs. inside-out?
13.14 Overloading prefix/postfix forms of operators ++ and --?
13.15 Which is more efficient: i++ or ++i?
[13.1] What's the deal with operator overloading?

It allows you to provide an intuitive interface to users of your class, plus makes it possible for templates to work equally well with classes and built-in/intrinsic types.

Operator overloading allows C/C++ operators to have user-defined meanings on user-defined types (classes). Overloaded operators are syntactic sugar for function calls: 

class Fred {
public:
  ...
};

#if 0

  // Without operator overloading:
  Fred add(Fred const& x, Fred const& y);
  Fred mul(Fred const& x, Fred const& y);

  Fred f(Fred const& a, Fred const& b, Fred const& c)
  {
    return add(add(mul(a,b), mul(b,c)), mul(c,a));    // Yuk...
  }

#else

  // With operator overloading:
  Fred operator+ (Fred const& x, Fred const& y);
  Fred operator* (Fred const& x, Fred const& y);

  Fred f(Fred const& a, Fred const& b, Fred const& c)
  {
    return a*b + b*c + c*a;
  }

#endif