Simple OO demonstration in C++, comparison to Python

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Simple OO demonstration in C++, comparison to Python

Archive - Originally posted on "The Horse's Mouth" - 2013-07-01 11:12:43 - Graham Ellis
From last week's quick introduction to C++ (a private course - half a day added on to the end of a C Programming course - an example of how C++ implements objects for a newcomer to C++ who's seen some Python.

Firstly, in C++ you must predefine the API - the interface between the user and the class. And also the member variables and methods of each object type too:

  class train {

    public:

      train(char *, int, int) ;

      int getpeeps();

    private:

      int length;

      int seats; };

Methods are defined in a similar way. In C++, there's no need to declare the object variable as a parameter (in fact you must not do so), but in the other hand you need to declare the class name on the front of each method. And the constructor is a method with the same name as the class. So:

  train::train(char *dest, int length, int spc) {

    this->length = length;

    this->seats = spc; }

  int train::getpeeps() {

    return (int)(this->length * this->seats * 1.4); }

Now for the application. You can create objects in several ways in C++; I chose to use the new keyword as it allocates memory on the heap in a similar way to Python allocates memory to objects

  swindon = new train("Swindon",5,83);

  cheltenham = new train("Cheltenham Spa",1,75);

And I can access that data via an object method.

  cattle = swindon->getpeeps();

  cout << "can take " << cattle << " to Swindon" << endl;

  cattle = cheltenham->getpeeps();

  cout << "can take " << cattle << " to Cheltenham" << endl;

If you prefer the "." notation of Python, I could replace
cattle = swindon->getpeeps();
with
cattle = (*swindon).getpeeps();
but that gets messy.

Complete C++ source code [here].