b) Write a recursive function reverse_num_rec to reverse an integer

#include <iostream>
#include <cmath>
using namespace std;

int reverse_num_rec (int n);

int main() {
  int n;
  cout << "Enter a number: " << endl;
  cin >> n;
  cout << "The reverse of the integer is " << reverse_num_rec(n) << endl;
}

int reverse_num_rec (int n) {
  if (n < 10) {
    return n;
  } else { 
    return 
  }
}