When the 'Add Player' operation is selected, the main function will ask the user to provide all the information of the new player, then it calls a user-defined function named addPlayer(...) to add the player to the file. Before the record is added to the file, two things must be checked:
o The provided team-letter must be in the range A-Z. This must be validated via another user- defined function named teamCodeIsValid(...); and a suitable error message should be displayed by the function addPlayer(...) if the letter is invalid.
o The number of the players in the specified team must be less than 11 before adding the new player. This must be counted and returned via another user-define function named countPlayers(...); and a suitable error message should be displayed if the team is already full.