01. Different Strings C++ Exam

#include <iostream>
#include <string>

int main()
{
    using namespace std;

    size_t len;
    cin >> len;

    string str1, str2;
    cin >> str1 >> str2;

    size_t num_diff = 0, sum_digits = 0;
    for (size_t i = 0; i < len; ++i)
    {
        if (str1[i] == str2[i])
            cout << str1[i];
        else if (isalpha(str1[i]) && isalpha(str2[i]) && abs(str1[i] - str2[i]) == 32)
            cout << __min(str1[i], str2[i]);
        //else if (toupper(str1[i]) == toupper(str2[i]))
        //  cout << (char)toupper(str1[i]);
        else
        {
            cout << '#';
            ++num_diff;
        }
        if (isdigit(str1[i]))
            sum_digits += str1[i] - '0';
        if (isdigit(str2[i]))
            sum_digits += str2[i] - '0';
    }

    cout << endl << num_diff << endl << len - num_diff << endl << sum_digits << endl;

    return 0;
}