Program to find GCD(Greatest common divisior) of two numbers using recursion

#include <iostream>
using namespace std; 

int gcd(int a, int b)
{
 if(b == 0)
 {
         return a;
 }
 else
 {
  return gcd(b, a % b);
 }
}

int main()
{
     int a,b;
          
     cout << "Input first number: ";
     cin >> a;
     cout << "Input second number: ";
     cin >> b;
     
     cout << "Greatest common divisior (GCD) is " << gcd(a,b) << endl;
     return 0;
}

Programe to Check Palindrome using recursion

#include<iostream>
using namespace std;
int palindrome(int num);

int main() {
   int num,number, val;
   cout<<"Enter a number: ";
   cin>>num;
   number=num; //save orignal number
   val = palindrome(num); //function call
   if(val==number) c//check returned value with orignal value/number
    cout<<"Number is Palindrome";
    else
     cout<<"Number is not Palindrome";
   return 0;
}
int palindrome(int num)
 {
     int rem;
     static int temp=0;
   if (num != 0)
   {
      rem =num%10;
      temp=(temp*10)+rem;
      palindrome(num/10); // recursive function call
   }
   return temp;
}

Programe to calculate sum of digits using recursion

#include<iostream>
using namespace std;
int calsum(int num);

int main() {
   int num, val;
   cout<<"Enter a number: ";
   cin>>num;
   val = calsum(num);
   cout<<"\nSum of the digits of "<<num<<" is "<<val;
   return 0;
}
int calsum(int num)
 {
   if (num != 0)
   {
      return num%10 + calsum(num/10);
   }
}

Output

 

Program to Check Prime Number Using Recursion

#include <iostream>
using namespace std;

int checkPrimeNumber(int);

int main()
{
  int n;
  cout << "Enter a positive  integer: ";
  cin >> n;
 
  if(checkPrimeNumber(n) == 0)
    cout << n << " is a prime number.";
  else
    cout << n << " is not a prime number.";
  return 0;
}
int checkPrimeNumber(int n)
{
  bool flag = false;
  for(int i = 2; i <= n/2; ++i)
  {
      if(n%i == 0)
      {
          flag = true;
          break;
      }
  }
  return flag;
}