int daysInMonth(int month, int year){
  int numberOfDays = ERROR_VALUE;
  switch(month){
    case 1: case 3: case 5: case 7: case 8: case 10: case 12: 
      numberOfDays = 31; break;
    case 4: case 6: case 9: case 11: 
      numberOfDays = 30; break;
    case 2:
      if (isLeapYear(year))
        numberOfDays = 29;
      else
        numberOfDays = 28;
      break;
  }
  return numberOfDays;
}