How can I fix the form size in a C# Windows Forms application and not to let user change its size?
Check this:
// Define the border style of the form to a dialog box.
form1.FormBorderStyle = FormBorderStyle.FixedDialog;
// Set the MaximizeBox to false to remove the maximize box.
form1.MaximizeBox = false;
// Set the MinimizeBox to false to remove the minimize box.
form1.MinimizeBox = false;
// Set the start position of the form to the center of the screen.
form1.StartPosition = FormStartPosition.CenterScreen;
// Display the form as a modal dialog box.
form1.ShowDialog();