How do I make a field mandatory?

Question

I am mounting an Engineering Management Application(Consoleapp) p/college... I would like to know how to make mandatory the entry of the fields Name/Surname/CPF/dataNascization when the user is adding a new person? Ah and I would like to know how to put the CPF to have 11 characters?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using CSharpUltimateASS;

namespace CSharpUltimateASS
{
    public class Pessoa
    {
        public string _nome;
        public string _sobrenome;
        public string _CPF;
        public DateTime _dataNascimento;

        public Pessoa(string nome, string sobrenome, string CPF, DateTime dataNascimento)
        {
            _nome = nome;
            _sobrenome = sobrenome;
            _CPF = CPF;
            _dataNascimento = dataNascimento;

        }
    }
}

Answer 1

To keep the solution of this in a way that meets the scope of your exercise, I made these changes to your code, but I did it in a way that is simple enough for your teacher not to think bad and of course, for you to learn too.

Since I don’t know how far your teacher has already taught you, I’m not going to modify anything in your class, I believe the goal of doing the "_" before the names is to create public property using private variables, but I’ll leave your code anyway.

I am creating here a static method that will return you an instance of the Person class, only if all fields are validated. Otherwise, it will return to you null

Notice that I put the constructor as private so the programmer is required to call the method GetInstancia

public class Pessoa
{
    public string _nome;
    public string _sobrenome;
    public string _CPF;
    public DateTime _dataNascimento;

    private Pessoa(string nome, string sobrenome, string CPF, DateTime dataNascimento)
    {
        _nome = nome;
        _sobrenome = sobrenome;
        _CPF = CPF;
        _dataNascimento = dataNascimento;
    }

    public static Pessoa GetInstancia(string nome, string sobrenome, string CPF, DateTime dataNascimento)
    {
        bool construir = true;

        if (nome == "")
        {
            Console.WriteLine("O nome é obrigatório.");
            construir = false;
        }

        if (sobrenome == "")
        {
            Console.WriteLine("O sobrenome é obrigatório");
            construir = false;
        }

        if (CPF == "")
        {
            Console.WriteLine("O CPF é obrigatório.");
            construir = false;
        }
        else if (CPF.Length != 11)
        {
            Console.WriteLine("O CPF é inválido.");
            construir = false;
        }

        if (dataNascimento == DateTime.MinValue)
        {
            Console.WriteLine("A data é obrigatória.");
            construir = false;
        }

        if(construir)
        {
            return new Pessoa(nome, sobrenome, CPF, dataNascimento);
        }
        else
        {
            return null;
        }
    }
}

Remember however that the purpose of this is only didactic!

I do not recommend putting Console.WriteLine within the class.

However, as the goal is to keep the simplicity, I see no problems.

Example of how to consume this method:

Pessoa _pessoa = Pessoa.GetInstancia("teste", "teste", "1234", DateTime.Now);

if(_pessoa != null)
{
  //Código para adicionar em uma lista.
}