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.
     Rules of Function Overloading

     // 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. To learn operator overloading in details visit this link.

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;    class base { public:     virtual void print ()     { cout<< "print base class" <<endl; }         void show ()     { cout<< "show base class" <<endl; } };     class derived:public base { public:     void print () //print () is already virtual function in derived class, we could also declared as virtual void print () explicitly     { cout<< "print derived class" <<endl; }         void show ()     { cout<< "show derived class" <<endl; } };    //main function int main()  {     base *bptr;     derived d;     bptr = &d;             //virtual function, binded at runtime (Runtime polymorphism)     bptr->print();              // Non-virtual function, binded at compile time     bptr->show();         return 0; }

     Output:

     print derived class
     show base class
     

     To learn runtime polymorphism in details visit this link.

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