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Exercise solution:
A template class with friends

Here is the header file point.h:

template<class C> class Point;
template<class C> std::ostream& operator<<(std::ostream& s, const Point<C>& p);

template<class C>class Point {
private: 
  C x, y;

public:
  Point(C, C);
  Point();
  C getx () const;
  C gety () const;
  Point<C>& move(C, C);
  C distance_to(Point);
  friend  std::ostream& operator<< <>(std::ostream&, const Point<C>&);
};

Notice the two declarations before the generic class point defintion. And notice the <> before the parameters in the friend declaration

Here is the point.cc:

#include <cmath>
#include <iostream>
#include "point.h"

template<class C> Point<C>::Point(C x_coord, C y_coord):
   x(x_coord), y(y_coord){
}

template<class C> Point<C>::Point(): x(0.0), y(0.0){
}

template<class C> C Point<C>::getx () const{
  return x;
}

template<class C> C Point<C>::gety () const{
  return y;
}

template<class C> Point<C>& Point<C>::move(C dx, C dy){
    x += dx; y += dy; 
    return *this;
}

template<class C> C Point<C>::distance_to(Point p){
    return sqrt((x - p.x) * (x - p.x) + (y - p.y) * (y - p.y));
}


template<class C> std::ostream& operator<<
                          (std::ostream& s, const Point<C>& p){
  return s << "(" << p.x << "," << p.y << ")" ;
}

Finally, prog.cc with main:

#include <iostream>
#include <string>
#include "point.cc"           // Notice inclusion of cc files, in order to 
                              // instantiate the templates for int and double.
                              // Else lots of linker errors will occur.
                              // This treats templates in the same way as inline functions.
                              // The C++ Programming Language, 3ed ed, page 350-351.
int main(){
  Point<double> pd1,
                pd2(1,2);

  Point<int>    pi1,
                pi2(3,4);

  Point<char>   pc1,
                pc2(97, 98);   // Char 97 = 'a'

  pd2.move(1,1);
  pi2.move(1,1),
  pc2.move(1,1),

  std::cout << "pd2: " << pd2 << std::endl;      // (2,3)
  std::cout << "pi2: " << pi2 << std::endl;      // (4,5)
  std::cout << "pc2: " << pc2 << std::endl;      // (b,c)
}