bulls_and_cows

// A little guessing game called
//    (for some obscure reason) <<Bulls and Cows>>.

#include <std_lib_facilities.h>

int count (const vector<char>& digits, char d)
{
  int k{};

  for (int i = 0; i < digits.size(); ++i)
    if (digits[i] == d)
      ++k;

  return k;
}

bool validate (const vector<char>& number)
{
  for (int i = 0; i < number.size(); ++i)
  {
    if (number[i] < '0' || '9' < number[i]){
      //error("the number contains not a digit");
      cout << "the number contains not a digit" << "\n";
      return 0;
    }

    if (count(number, number[i]) != 1){
      //error("digits of the number are not unique");
      cout << "digits of the number are not unique" << "\n";
      return 0;
    }

  }
  return 1;
}

vector<char> user_guess ()
{
  vector<char> number(4);
  bool ok = 0;
  while (!ok) {
    cout << "guess the number: ";
    for (int i = 0; i < number.size(); ++i)
    cin >> number[i];
    ok = validate(number);
  }


  if (!cin)
    error("invalid input");



  return number;
}

#include <cstdlib>
#include <ctime>

int main () {
  try
  {
    cout << "<<Bulls and Cows>>\n"
        << "Computer sets a number of 4 unique digits.\n"
        << "Try to guess it.\n"
        << "<Bull> means right digit in the right position.\n"
        << "<Cow> means right digit in the wrong position.\n"
        << "\n"
        << "game is on" << endl;

    srand((unsigned)time(0));
    vector<char> number{char(rand() % 10), char(rand() % 10), char(rand() % 10), char(rand() % 10)};

    int bulls{};

    do
    {
      bulls = 0;
      int cows{};

      vector<char> uguess = user_guess();

      for (int i = 0; i < uguess.size(); ++i)
      {
        if (uguess[i] == number[i])
          ++bulls;
        else if (count(number, uguess[i]) == 1)
          ++cows;
      }

      cout << bulls << " bull(s) and " << cows << " cow(s)" << endl;
    }
    while (bulls != 4);

    cout << "game is over" << endl;
  }
  catch (exception& e)
  {
    cerr << e.what() << endl;
    return 1;
  }
  catch (...)
  {
    cerr << "Oops, something went wrong..." << endl;
    return 2;
  }
}