c# List and object

Question

I want to create a new user and save it in my list. Im new in C#, and I don´t know how I´m going to solve this. I´m using list.

using MetroFramework.Forms;
    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    using System.Windows.Forms;


        namespace SGE
        {
            public partial class Registar_Utilizador : MetroForm
            {
                string username, password, tipo;
                List<Pessoa> todos = new List<Pessoa>();
                List<Pessoa> novaListaPessoa = new List<Pessoa>();

                public Registar_Utilizador(List<Pessoa> todos)
                {
                    InitializeComponent();
                }

                private void metroButtonAdicionar_Click(object sender, EventArgs e)
                {
                    int i = 0;
                    Pessoa p = new Pessoa();
                    do
                    {
                        p.setusername(metroTextBoxUsername.Text);
                    }while(i < todos.Count && p.getusername() == todos[i++].getusername());

                }
            }
        }

[Error] Error 1 Use of unassigned local variable 'todos'

Answer 1

In your Registar_Utilizador, you don't need to pass the list. You are doing nothing with it that I see.

public Registar_Utilizador(List<Pessoa> todos)
            {
                InitializeComponent();
            }

Now for this method: you will change it to below - I have shown using foreach:

 private void metroButtonAdicionar_Click(object sender, EventArgs e)
 {        
    foreach(Pessoa p in todos)
    {
        if (someCondition) //p.getusername() == todos[i++].getusername()
        {
          p.setusername(metroTextBoxUsername.Text);
          novaListaPessoa.Add(p)
        }
    }   
}

if you want to create a new instance of objects in todos, then you can use information from here to copy one object to another copy one object to another