Polymorphism in C++

The word polymorphism means having many forms. In simple words, we can define polymorphism as the ability of a message to be displayed in more than one form.
Real life example of polymorphism, a person at a same time can have different characteristic. Like a man at a same time is a father, a husband, a employee. So a same person posses have different behavior in different situations. This is called polymorphism.
Polymorphism is considered as one of the important features of Object Oriented Programming.
In C++ polymorphism is mainly divided into two types:

  • Compile time Polymorphism
  • Runtime Polymorphism
  1. Compile time polymorphism: This type of polymorphism is achieved by function overloading or operator overloading.
    • Function Overloading: When there are multiple functions with same name but different parameters then these functions are said to be overloaded. Functions can be overloaded by change in number of arguments or/and change in type of arguments.
      // C++ program for function overloading
      #include <bits/stdc++.h>
      using namespace std;
      class Geeks
      {
          public:
          
          // function with 1 int parameter
          void func(int x)
          {
              cout << "value of x is " << x << endl;
          }
          
          // function with same name but 1 double parameter
          void func(double x)
          {
              cout << "value of x is " << x << endl;
          }
          
          // function with same name and 2 int parameters
          void func(int x, int y)
          {
              cout << "value of x and y is " << x << ", " << y << endl;
          }
      };
      int main() {
          
          Geeks obj1;
          
          // Which function is called will depend on the parameters passed
          // The first 'func' is called
          obj1.func(7);
          
          // The second 'func' is called
          obj1.func(9.132);
          
          // The third 'func' is called
          obj1.func(85,64);
          return 0;
      }

      Output:

      value of x is 7
      value of x is 9.132
      value of x and y is 85, 64
      

      In the above example, a single function named func acts differently in three different situations which is the property of polymorphism.

    • Operator Overloading: C++ also provide option to overload operators. For example, we can make the operator (‘+’) for string class to concatenate two strings. We know that this is the addition operator whose task is to add to operands. So a single operator ‘+’ when placed between integer operands , adds them and when placed between string operands, concatenates them.
      Example:

      // CPP program to illustrate
      // Operator Overloading
      #include<iostream>
      using namespace std;
       
      class Complex {
      private:
          int real, imag;
      public:
          Complex(int r = 0, int i =0)  {real = r;   imag = i;}
           
          // This is automatically called when '+' is used with
          // between two Complex objects
          Complex operator + (Complex const &obj) {
               Complex res;
               res.real = real + obj.real;
               res.imag = imag + obj.imag;
               return res;
          }
          void print() { cout << real << " + i" << imag << endl; }
      };
       
      int main()
      {
          Complex c1(10, 5), c2(2, 4);
          Complex c3 = c1 + c2; // An example call to "operator+"
          c3.print();
      }

      Output:

      12 + i9
      

      In the above example the operator ‘+’ is overloaded. The operator ‘+’ is an addition operator and can add two numbers(integers or floating point) but here the operator is made to perform addition of two imaginary or complex numbers.

  2. Runtime polymorphism: This type of polymorphism is achieved by Function Overriding.
    • Function overriding on the other hand occurs when a derived class has a definition for one of the member functions of the base class. That base function is said to be overridden.
      // C++ program for function overriding
      #include <bits/stdc++.h>
      using namespace std;
      // Base class
      class Parent
      {
          public:
          void print()
          {
              cout << "The Parent print function was called" << endl;
          }
      };
      // Derived class
      class Child : public Parent
      {
          public:
          
          // definition of a member function already present in Parent
          void print()
          {
              cout << "The child print function was called" << endl;
          }
          
      };
      //main function
      int main()
      {
          //object of parent class
          Parent obj1;
          
          //object of child class
          Child obj2 = Child();
          
          
          // obj1 will call the print function in Parent
          obj1.print();
          
          // obj2 will override the print function in Parent
          // and call the print function in Child
          obj2.print();
          return 0;
      }

      Output:

      The Parent print function was called
      The child print function was called
      

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rakesh

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