Passing variables between forms using a button [duplicate]

Answer 1

In your code have a variable accessible by both forms. For example create a new Namespace and add a public static class FormData with a public static int Value inside.

namespace GlobalVariables
{
  public static class FormData
  {
    public static int Value { get; set; }
  }
}

Then from both of your forms you can access the said variable (and modify it) with GlobalVariables.FormData.Value. Here I made it a property, but you can do pretty much whatever you want with it.