Prac_Login.cs

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

namespace MyForm
{
    class Login:Form
    {
        private Button btLogin; //private because it's an attribute to the class. an object so no need for properties
        private TextBox username;
        private TextBox password;
        private Label un;
        private Label pw;


        public Login()
        {
            InitializeComponents();
        }

        public void InitializeComponents()
        {
            this.Text = "Login Form";
            this.BackColor = Color.Lavender;
            this.ForeColor = Color.Black;
            this.Size = new Size(250, 300);
            this.StartPosition = FormStartPosition.CenterScreen;


            btLogin = new Button();
            btLogin.Text = "Login";
            btLogin.Location = new Point(70,150);
            btLogin.Click += btLogin_Click;

            un = new Label();
            un.Text = "Username";
            un.Location = new Point(20,80);

            username = new TextBox();
            username.Text = "";
            username.Location = new Point(80,80);

            pw = new Label();
            pw.Text = "Password";
            pw.Location = new Point(20,110);

            password = new TextBox();
            password.Text = "";
            password.PasswordChar = '*';
            password.MaxLength = 10;
            password.Location = new Point(80,110);

            this.Controls.Add(username);
            this.Controls.Add(password);
            this.Controls.Add(btLogin);
            this.Controls.Add(un);
            this.Controls.Add(pw);
        }

        public void btLogin_Click(object sender, EventArgs e)
        {
            DialogResult dr = MessageBox.Show("Enter Main Form?", "Login", MessageBoxButtons.YesNo, MessageBoxIcon.Asterisk);
            if (dr == DialogResult.Yes)
            {
                MainForms mf = new MainForms(username.Text); //this is just an instance
                mf.Show();
                this.Hide();

            }
            else
                MessageBox.Show("Goodbye.");
        }
    }

    class MainForms:Form
    {
        public MainForms(string username)
        {
          this.Text = username;
          this.FormClosing += ThisOnFormClosing;
        }

        public void ThisOnFormClosing(object sender, FormClosingEventArgs e)
        {
            Login myLogin = new Login();
            myLogin.Show();
        }
    }
}