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. A real-life example of polymorphism, a person at the same time can have different characteristics. Like a man at the same time is a father, a husband, an employee. So the same person posses 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
Polymorphism-in-CPP

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 Prutor
{
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() {

Prutor 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 two 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