function checkDate() {
  //First if statement checks that day is within 1 and 31, the maximum and minumum amount of days in a month
  if (birthDay >= 1 && birthDay <= 31) {
    //Ensures that the entered day is possible for said month.
    if ( birthMonth == "January" || birthMonth == "March" || birthMonth == "May" || birthMonth == "July" || birthMonth== "August" || birthMonth == "October" || birthMonth== "December"  && birthDay<=31 ) {
      validDate = 1;
    }
    if (birthMonth == "February" && birthDay<=29 ) {
      validDate = 1;
    }
    if (birthMonth == "April" && birthDay<=30 ) {
      validDate = 1;
    }
  } else {
    //If not a real day, valid date is set to zero
    validDate = 0;
  }
}