Why does 'Hello, World!' compile even though other code was entered?

Question

C++ / C#

For some reason, another message is being compiled, what's the matter?
Actually, it's hardly a matter of the code, rather I'm crooked)

#include "std_lib_facilities.h"
int main()
{
  cout << "Введите ваше имя(и нажмите 'enter'):\n";
  string firts_name;
  cin >> firts_name;
  cout << "Привет, << first_name << "!\n";
}

Answer 1

cout << "Hi, << first_name << "!\n";

I see an error. You also take a look.
Apparently, the compilation fails and the last working version of the program is launched.

Answer 2

cout << "Привет, " << first_name << "\n";

Answer 3

The Visual Studio C++ compiler needs some time to warm up, so the Kernighan-Ritchie bookmark can compile a certain number of times, this is your very Hello World.