18. Conversion by constructor

• Defining a constructor which takes one argument of type T gives conversion from T to your type:

  
  // rational.h
  class Rational {
  private:
      int m_n;
      int m_d;
  public:
      Rational( int num ) // convert int to Rational
          : m_n(num), m_d(1)
      {
      }
  };
  
  void print_rational( Rational const& rat );
  
  // main.cpp
  #include "rational.h"
  int main( )
  {
      Rational rat = 3;  // Ok: same as r(3)
      print_rational(3); // Ok: one-level implicit conversion
      return 0;
  }