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How to set a form as the Main Loading form Windowsforms

I have one form let's call it registration which i created first, I now have a second form lets call it menu. I know these were created the wrong way around but now when i run my Win-forms application it only ever loads the registration form , i am trying to switch my Menu form to be the main loading form (to which i will add a function/button to then load the registration form). I have tried looking in the panel to perhaps set a parent/child relationship cant but find anything

In the Program.cs there is a method called Main.
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
// ^^^^^
}
Change the Form1 to the other form you wish to create at startup.

Windows form application not closing

I am making a Windows form app in c# and the process is never killed after I close the main form. The process sits in the background, taking up memory. I have tried many methods, such as Application.exit and Environment.exit, none of which have worked.
I have tried:
private void Form1_FormClosing(Object sender, FormClosingEventArgs e)
{
Environment.Exit(0);
}
And
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
Environment.Exit(0);
}
}
I have tried both methods using both Application.Exit and Environment.Exit
I just want a solution that kills the process upon closing the main form
EDIT:
Upon closer inspection, this error only occurs when a button is pressed that switches to my project's second form using:
Form2 f = new Form2();
f.Show();
this.Hide();

I have used:
Environment.Exit(0);
Application.Exit();
and it was working for me on a project of mine.

If it isn't already, you need to mark your main method with [STAThread] attribute (see https://stackoverflow.com/a/1361048/1497128), like so --
[STAThread]
private static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}
If it is, then make sure that...
... all foreground threads are being terminated before the form closes
... if you subscribe to FormClosing event then ensure you are not setting Cancel = true
Neither of your solutions are necessary, WinForm applications terminate the process when the main form is closed (assuming nothing else is blocking, such as another foreground thread). You can test this by creating a new WinForm project in Visual Studio, running it and closing the form.
Unless you are using specific logic to control when the application should exit, you definitely shouldn't need Environment.Exit(0) (mainly used for console apps) nor Application.Exit() (used with WinForm apps). Closing the form should do it, which can be done programmatically by calling form.Close().

when using a button click to open a new form use USING
using (Form1 frm = new Form())
{
frm.ShowDialog();
}

How to close a form launched from Main() without cross-thread errors

I have an Windows form application that can be called from command line or used as a GUI. The command line options are only for scheduling the program to run saved tasks, so I don't want the GUI to launch if the command line options are used.
static void Main()
{
//code to parse the command line options
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
try
{
Application.Run(new MainForm());
}
}
public MainForm()
{
//Loading data from a file into the form.
If (ArgumentList.Length >0)
{
//do command line-requested tasks
this.close();
}
else
{
//do GUI tasks
}
}
How do I close the MainForm window without making a instance of ObjectDisposedException be thrown? If I use anything after
Application.Run(new MainForm());
it doesn't run because that form is opened and nothing runs after that line until the form is closed. I've tried
this.Hide();
instead of
this.Close();
but this.Hide() doesn't seem to do anything in this case, as the form still shows. I know that I shouldn't try to close a form from within the form (cross-threading), but if I don't want the GUI form to show if called from command line.

You should move that code to Main(), and avoid the form entirely if you don't need it.

How to close a form, exit all process and open another form

How do I close a form and exit all the functions in that form and open another form?
I tried using application.exit(), I need something like that. But the problem is it shuts down all the forms and process, I need to end all the process in a form and close it and go to another form

In the program.cs file of your project, your main function would be something like
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}
Your execution ends when you close Form1.
You can change it to something like
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
Application.Run(new Form2());
}
Now in this case, when you close Form1, the execution would not end, but instead it will open Form2 and the program will run as long as form2 is open.

My form is not opening in STA

I'm trying to open my main form, from my login form.
Application.Run(new Form1(usernameText.Text));
But it's not opening in STA.. So my folderBrowserDialog1 in my main form won't open. And I have [STAThread] in my program.cs just above static void Main() And it still does not work... So I'm not sure what to do...
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new loginForm());
}

Here is Servy's response to your similar question:
Go to your program.cs file and alter it so that you show your login form. Then, after it has been closed, determine if you should open up another form.
It'll likely look something like this:
LoginForm loginform = new LoginForm();
Application.Run(loginform);
if (loginform.DialogResult == DialogResult.Yes)
Application.Run(new MainForm());
//TODO handle error cases