15. Common uses of operators

• Most classes need =, many need ==, some need >.

• Numerical classes gain natural syntax of arithmetic operators.

• String classes provide + and += for concatenation, and [ ] for character access.

• Lookup structures add operator[ ] taking key types:

  
  // PhoneBook.h
  class PhoneBook {
  public:
      string const& operator[]( string const& key );
      //...
  };
  
  // main.cpp
  #include <iostream>
  #include "PhoneBook.h"
  using namespace std;
  int main( )
  {
      PhoneBook pb;
      //...
      cout << "Bob's number is " << pb[ "Bob" ] << endl;
      return 0;
  }