Introduction to Object Oriented Programming Concepts in C++

Updated on September 8, 2015     Kisan Patel

Class

• Class — group of data members & member functions.
• Like person can be class having data members height and weight and member functions as get_details() and put_details() to manipulate on details.
• Class is nothing until you create it’s object.

Object

Access to data members & member functions can be done using object only (if they are not static!).

OOPS features are —

• Encapsulation
• Data hiding
• Data reusability
• Overloading (polymorphism)
• Overriding

Encapsulation

• making one group of data members & member functions.
• Can be done through class
• Then group of data members & Member functions will be available just by creating object.

Data hiding

• can be done through access modifiers.
• Access modifiers are private, public, protected and internal.
• Private members are member function won’t be available outside class.
• Public — available all over in program outside class also.
• Protected — members that are available in class as well as in it’s child class.
• Protected access modifier comes only when inheritance is in picture.
• Internal is used with assembly creation.

class employee {
        private:
            char empname[50];
            int empno;
        
        public:
            void getvalue()  
            {
               cout<<"INPUT Employee Name:";
               cin>>empname;
               cout<<"INPUT Employee Number:";
               cin>>empno;  
            }
        void displayvalue()
        {
            cout<<"Employee Name:"<<empname<<endl;
            cout<<"Employee Number:"<<empno<<endl;
        }
};
main()
{
   employee e1;
   e1.getvalue();
   e1.displayvalue();
}

Overloading

• taking different output of one method or operator based on parameters and return types.
• Like add() method performs addition and add(int a, int b) performs addition of ‘a’ and ‘b’ passed when calling.
• Also, + operator performs addition of two numbers as well as concatenation of strings.

class arith
{
   public:
        void calc(int num1)
        {
           cout<<"Square of a given number:"<<num1*num1<<endl;
        }

   void calc(int num1, int num2)
   {
      cout<<Product of two whole numbers:"<<num1*num2<<endl;
   }
};
int main() //begin of main function
{
    arith a;
    a.calc(5);
    a.calc(6, 7);
}

Data reusability (inheritance)

• helps in saving developers time.
• You can use already created class to create new one.
• Called inheritance
• Already existing class is base class and new created is derived class.
• Base class members can be available in derived class and to access them create object of derived class like from parent to child.

class CPolygon
{
     protected:
         int width, height;
     public:
         void set_values(int a, int b)  {
                width = a; height= b;
         }
};
class CRectangle: public CPolygon
{
     public: int area() {
         return (width * height);     
     }
};
class CTriangle : public CPolygon
{
     public: int area() {
         return (width * height / 2);
     }
};
int main()
{
     CRectangle rect;
     CTriangle trgl;
     rect.set_values(4, 5);
     trgl.set_values(4, 5);
     cout<<trgl.area()<<endl;
     cout<<trgl.area()<<endl;
     return 0;
}

Overriding

• In C++, overriding is a concept used in inheritance which involves a base class implementation of a method.
• Then in a subclass, you would make another implemantation of the method. This is overriding. Here is a simple example.

class Base
{
   public:
       virtual void DoSomething() { x = x + 5; }

   private:
       int x;
};
class Derived : public Base
{
   public:
       virtual void DoSomething() { y = y + 5; Base:DoSomething(); }
   private:
       int y;
}