How to use expanded property in C#

Question

I have a problem, I created a class containing the following property:

public class MinhaClasse
{
public int Idade {get; set;}
}

But when I do it:

public class MinhaClasse
{
   public int Idade {
      get{
         return Idade;
      }
      set{
         if (value < 18)
            throw new Exception("Proibido para menores!");
         else
            Idade = value;
      }
   }
}

The above code does not work and I am obliged to create a private attribute to store the value idade, or at least I have done so. Is that correct? Why can’t I use Idade = value?

public class MinhaClasse
    {
       private int _idade;
       public int Idade {
          get{
             return _idade;
          }
          set{
             if (value < 18)
                throw new Exception("Proibido para menores!");
             else
                _idade = value;
          }
       }
    }

Answer 1

You have to create the private field to work, you are creating a loop infinite, because the property is used Idade to manipulate property Idade, which will then force you to manipulate Idade and so it goes.

using System;

public class Program {
    public static void Main() {
        var obj = new MinhaClasse();
        obj.Idade = 20;
        Console.WriteLine(obj.Idade);
        obj.Idade = 10;
        
    }
}

public class MinhaClasse {
    private int idade;
    public int Idade {
        get => idade;
        set => idade = value < 18 ? throw new Exception("Proibido para menores!") : value;
    }
}

Behold working in the ideone. And in the .NET Fiddle. And in the Coding Ground. Also put on the Github for future reference.

Every time you throw a Exception is doing something wrong. They even consider that this class should be abstract so that no one can use it. Many people consider it bad to make an exception on a property, at least in most cases. This is control flow with exception.