text: #include <iostream>
  #include <vector>
  #include <string.h>
  
  int main(int argc, char** argv)
  {
      if (argc == 1) {
          std::cout << "Hello world!\n"; 
      } else if (argc == 2) {
          std::cout << argv[1] << "\n"; 
      } else {
          return 1;
      }
  }