Program to check EVEN or ODD using Recursion in C++

#include <iostream>
using namespace std;

//function prototype/declaration
int isEven(int);

int main() 
{

	int n;
	
	cout<<"Enter a number: ";
	cin>>n;

	if(isEven(n))
		cout<<"It is an EVEN Number";
	else
		cout<<"Is is an ODD Number";	

    cout<<endl;
	return 0;
}

//function definition/body
int isEven(int n)
{
	if(n == 0)
		return 1;
	else if(n == 1)
		return 0;
	else if(n<0)
		return isEven(-n);
	else
		return isEven(n-2);		
}

Output

First run:
Enter a number: 101 
Is is an ODD Number 

Second run:
Enter a number: 120 
It is an EVEN Number 

In this program we are using the function recursion technique. We are recurring function until the value of n is either 1 or 0. If it ends at one of these values, the function returns 1 for even number and 0 for not even.

We have called the function inside of if statement. When the number is true, the function returns 1 and the result of if expression is true and similar is the case of non-even number.