Intro to Classes - C++

classes.cpp

#include <iostream>

using namespace std;

class Computer // Standard way of defining the class
{
public:
  // This means that all of the functions below this(and any variables)
  //  are accessible to the rest of the program.
  //  NOTE: That is a colon, NOT a semicolon...
  Computer();
  // Constructor
  ~Computer();
  // Destructor
  void setspeed ( int p );
  int readspeed();
protected:
  // This means that all the variables under this, until a new type of
  //  restriction is placed, will only be accessible to other functions
 in the
  //  class.  NOTE: That is a colon, NOT a semicolon...
  int processorspeed;
};
// Do Not forget the trailing semi-colon

Computer::Computer()
{
  //Constructors can accept arguments, but this one does not
  processorspeed = 0;
}

Computer::~Computer()
{
  //Destructors do not accept arguments
}

void Computer::setspeed ( int p )
{
  // To define a function outside put the name of the class
  //  after the return type and then two colons, and then the name
  //  of the function.
  processorspeed = p;
}
int Computer::readspeed()  
{
  // The two colons simply tell the compiler that the function is part
  //  of the class
  return processorspeed;
}

int main()
{
  Computer compute;  
  // To create an 'instance' of the class, simply treat it like you would
  //  a structure.  (An instance is simply when you create an actual object
  //  from the class, as opposed to having the definition of the class)
  compute.setspeed ( 100 ); 
  // To call functions in the class, you put the name of the instance,
  //  a period, and then the function name.
  cout<< compute.readspeed();
  // See above note.
}