Question

I need to change a button text using an static function.

static string[] ARRay = new string[10];
[STAThread]
static void Main()
{
    string[] args = Environment.GetCommandLineArgs();
    for (int i = 1; i != args.Length; ++i)
    {
        command(i.ToString());
        ARRay[0] = i.ToString(); 
    }
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);
    Application.Run(new Form1());
}

static void command(string line)
{
    button1.Text = ARRay[0]; // here error
}

Answer 1

First of all, button1 seems to be the member of the Form Form1. You need to first store the Form1 instance in the Main method by first declaring a static member:

static Form1 myForm;

and then creating and passing that instance to Run method of Application:

myForm = new Form1();
Application.Run(myForm);

After you do this, you will have two options:
1. If button1 is a public Button, you can use this line in your command method:

myForm.button1.Text = ARRay[0];

Or 2. You can declare a public method in Form1 class to update the button1.Text.