Can comeone expain me with the function of this program

Question

#include<iostream>
using namespace std;
int add(int n);
int main()
{
int n; cout << "Enter a positive integer: ";
cin >> n;
cout << "Sum = " << add(n);
return 0;
}
int add(int n)
{
if(n != 0) return n + add(n - 1);
return 0;
}

Answer 1

This add function recursively adding number from 1 to the number the number provided by user.

If input number is 5 then program will add numbers in below fashion using recursion,
5+4+3+2+1
So output will be 15.