String function formula used

#include <iostream>
#include <cstring>

using namespace std;

int main()
{
    char string1[] = "Hello C++.";
    char string2[] = {'W', 'e',  'l', 'c', 'o', 'm', 'e', ' ', '!', '\0'};
    char string3[20];

    cout << string1 << endl;
    cout << string2 << endl;
    strcpy(string3,string1);
    cout << string3 << endl;
    strcat(string3,string2);
    cout << string3 << endl;
    cout << "The length of string3 is " << strlen(string1) << endl;


    return 0;
}