Add two number using function

#include <iostream>

using namespace std;

int add()

{

    int n1,n2,n3;

    cout<<"Enter a positive integer: ";

     cin>>n1>>n2;

n3=n1+n2;

return n3;

}

int sum;

    sum=add ();

        cout<<" sum= "<<sum;

  return 0;

       

}