Sum of digits with recursive function - C++

#include<iostream>
using namespace std;
int sum (int a);

int main()
{
    int num, result;

    cout<<"\n Enter Numbers : ";
    cin>>num;
    result = sum(num);
    cout<<"\n Sum of Digits : "<<result;
    return 0;
}
int sum (int num)
{
    if (num != 0)
    {
        return (num % 10 + sum (num / 10));
    }
    else
    {
       return 0;
    }
}