Question

can we have a single global variable which can be manipulated by multiple forms

Answer 1

You can access a single variable from any form, if it is declared as public.

If you are defining it in form1 and want to use it in form2, then from inside form2 you can call the variable as – form1.<variable_name>

Take an example-

Form1 code

Public Class Form1

Public a As Integer = 10

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Form2.Show()
End Sub

End Class

Form 2 code
Public Class Form2

Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    MsgBox(Form1.a)
End Sub

End Class