Most of what you need to know about classes

main.cpp

// class examples
// author : Tevin Thuku
// Date: 3rd: Dec: 2016

class Square {
   public:
      double length;  
      double width;  
};

int main( ) {
   Square Square1;  
   Square Square2;     
 
   // square1 specification
   Square1.length = 5.0; 
   Square1.width = 5.0; 

   // Square2 specification
   Square2.length = 10.0;
   Square2.width = 10.0;
	
   // area of Square1
   area = Square1.length * Square1.width;
   cout << "Area of Square1 : " << area <<endl;

   // area of Square2
   area = Square2.length * Square2.width;
   cout << "Area of Square2 : " << volume <<endl;
	
   return 0;
}

// FRIEND FUNCTIONS
// FULL EXAMPLE

class Name {
   string name;
public:
   friend void printName( Name firstname );
   void setName( string name );
};

// Member function definition
void Name::setName( string name ) {
   name = name;
}

// Note: printWidth() is not a member function of any class.
void printName( Name firstname ) {
   /* Because printWidth() is a friend of Box, it can
   directly access any member of this class */
   cout << "My name is : " << firstname.name <<endl;
}
 
// Main function for the program
int main( ) {
   Name firstname;
 
   // set box width with member function
   firstname.setName('ser arthur dayne');
   
   // Use friend function to print the wdith.
   printName( firstname );
 
   return 0;
}


// destructors and constructors

// REFERENCED FROM TUTORIALSPOINT.. CONSTRUCTORS AND DESTRUCTORS

#include <iostream>
 
using namespace std;
 
class Line {
   public:
      void setLength( double len );
      double getLength( void );
      Line(double len);  // This is the constructor
 
   private:
      double length;
};
 
// Member functions definitions including constructor
Line::Line( double len) {
   cout << "Object is being created, length = " << len << endl;
   length = len;
}
 
void Line::setLength( double len ) {
   length = len;
}
 
double Line::getLength( void ) {
   return length;
}

// Main function for the program
int main( ) {
   Line line(10.0);
 
   // get initially set length.
   cout << "Length of line : " << line.getLength() <<endl;
	
   // set line length again
   line.setLength(6.0); 
   cout << "Length of line : " << line.getLength() <<endl;
 
   return 0;
}