c# - Cannot implicitly convert type 'customtype' to 'othercustomtype'

Question

I am new to C#. I have a Persons class and a User class which inherits from the Persons class. I my console I input a users in an array. Then I can add a note to a user that is in the users array by only entering the users id. In my Persons class i have this function that has to search if this user is in the users array.

public static Persons FindPerson(Persons[] persons, int noteid)
{
    foreach (Persons person in persons)
        if (person.ID == noteid) return person;
    return null;
}

In my User class I have a function that loops the whole input of the id until it gets an id that is in the users array.

public static User SelectUser(User[] users)
{
    while (true)
    {
        Console.Write("Please enter the User id: ");
        string input = Console.ReadLine();
        int id;
        if (int.TryParse(input, out id))
        {
            Persons person = Persons.FindPerson(users, id);
            if (person != null) return person; // fail on "return person"                   
        }
        Console.WriteLine("The User does not exist. Please try again.");                
    }
}

Everything works fine except that I now get this error message on the "return person" in the if statement.

Cannot implicitly convert type 'UserCustomerNotes.Persons' to 'UserCustomerNotes.User'. An explicit conversion exists (are you missing a cast?)

Can anyone please help? Thanks in advance.

Answer 1

Because a Person is not nessecarily a User, the compiler is not able to implicitly convert a Person to a User. In your particular case, since you know you have a list of Users, you can explicitly tell it, "I know this Person is actually a User" with the following:

if (person != null)
   return (User) person;

The cast ((User)) will throw an exception at runtime if the instance is not actually a User, but since you've started with a collection of Users to begin with, you don't need to worry.