Lower to Upper and vice versa

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int i;
    string a,up,lo;
    getline(cin,a);
    for(i=0;a[i];i++){
        if(isupper(a[i])){
            lo.push_back(a[i]+32);
        }
        else{
            up.push_back(a[i]-32);
        }
    }
    cout<<"Upper = "<<up<<endl;
    cout<<"Lower = "<<lo<<endl;
    return 0;
}