maximilizuj i tryb pełno ekranowy

public partial class Form1 : Form
{
    bool Maximize, Fullscreen;
    Size OldSize;
    Point OldPos;

    public Form1()
    {
        InitializeComponent();
        Maximize = this.WindowState == FormWindowState.Maximized;
        Fullscreen = false;
    }

    private void GoMaximize()
    {
        Maximize = !Maximize;
        this.WindowState = Maximize ? FormWindowState.Maximized : FormWindowState.Normal;
    }

    private void GoFullscreen()
    {
        Fullscreen = !Fullscreen;

        if (Fullscreen)
        {
            Form f = new Form();
            
            OldSize = this.Size;
            OldPos = this.Location;

            this.Owner = f;
            this.FormBorderStyle = FormBorderStyle.None;
            this.Left = this.Top = 0;
            this.Width = Screen.PrimaryScreen.Bounds.Width;
            this.Height = Screen.PrimaryScreen.Bounds.Width;
            f.Show();
        }
        else
        {
            Form f = this.Owner;
            this.Owner = null;
            f.Close();

            this.FormBorderStyle = FormBorderStyle.Sizable;
            this.Location = OldPos;
            this.Size = OldSize;
        }
    }

    private void button1_Click(object sender, EventArgs e)
    {
        GoMaximize();
    }

    private void button2_Click(object sender, EventArgs e)
    {
        GoFullscreen();
    }
}