Запросить у пользователя имя, фамилию, а затем вывести строку вида "фамилия, имя"

#include <iostream>
#include <cstring>
int main()
{
    using namespace std;
 
    char fn[20];
    char ln[20];
    char z[2]{ "," };
    char p[2]{ " " };
 
    cout << "Enter your first name: ";
    cin >> fn;
    cout << "Enter your last name: ";
    cin >> ln;
    
    int md = strlen(fn) + strlen(ln) + strlen(z) + strlen(p) + 1;
 
    strncat(ln, ", ", md);
    strncat(ln, fn, md);
 
    cout << "Here\'s the information in a single string: " << ln << endl;
 
    return 0;
}

#include <iostream>
#include <cstring>
 
int main ()
{
    char fn [20];
    char ln [20];
 
    std::cout << "Enter your first name: ";
    std::cin >> fn;
    std::cout << "Enter your last name: ";
    std::cin >> ln;
    
    strcat (ln, ", ");
    strcat (ln, fn);
 
    std::cout << "Here\'s the information in a single string: " << ln;
    return 0;
}

#include <iostream>
#include <cstring>
 
int main ()
{
    std::string str1, str2;
    
    std::cout << "Enter your first name: ";
    std::cin >> str1;
    std::cout << "Enter your last name: ";
    std::cin >> str2;
    
    str2 = str2 + ", " + str1;
    
    std::cout << "Here\'s the information in a single string: " << str2;
    return 0;
}

#include <iostream>
#include <string>
 
int main()
{
    using namespace std;
    char fname[20], lname[50];
    cout << "Enter your first name: ";
    cin.getline(fname, 20);
    cout << "Enter your last name: ";
    cin.getline(lname, 20);
    strcat_s(lname, ", ");
    strcat_s(lname, fname);
    cout << "Here's the information in a single string: " << lname << endl;
    cin.get();
    cin.get();
    return 0;
}