#include <iostream>
using namespace std;


bool is_correct(int); // A FUNCTION PROTOTYPE

int main() {

   bool correct = false; // A VARIABLE LOCAL
                         // TO main
   int year;  // INTEGER VARIABLE

   while(!correct) { // ! STANDS FOR "NOT"
      cout << "Enter the year you were born> ";
      cout.flush();
      cin >> year;
      if (!cin) {
         cout << "Invalid input!" << endl;
         return 1;
      }
      correct = is_correct(year);
      if (correct) break;
      cout << "You could not be born in " << year 
           << '!' << endl;
   }

   cout << "You are " << (1999 - year) 
        << " years old." << endl;
  
   return 0;
}

bool is_correct(int year) { // IMPLEMENTATION 
   return year >= 1899 && year <= 1985;
}