How to access different variables in different subs? - input

Question

I've been trying to make a calculator on Visual Studio 2012 Ultimate. I've been trying to create different buttons, one asking for first number, second asking for second number, third asking for the operator and the last one displaying the answer in a message box. But whenever I try calling an Integer from another sub, it just doesn't work. I've tried making the sub Public. Here is my code :
Public Class Form1
Public Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim prompt1, title1 As String
Dim a As Integer
prompt1 = "Enter First Number : "
title1 = "First Number"
a = InputBox(prompt1, title1)
End Sub
Public Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
Dim prompt2, title2 As String
Dim b As Integer
prompt2 = "Enter Second Number : "
title2 = "Second Number"
b = InputBox(prompt2, title2)
End Sub
Public Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
Dim prompt3, title3 As String
Dim op As String
Dim ans As Integer
prompt3 = "Enter Operator : "
title3 = "Operator"
op = InputBox(prompt3, title3)
If op = "+" Then
ans = a +
End If
End Sub
Public Sub Button4_Click(sender As Object, e As EventArgs) Handles Button4.Click
End Sub
End Class
As you can see I've not completed it because I can't call a in the third button.
Any ideas ?
If I'm messing up, please point it out.

Answer 1

define variable a outside of button1
Public Class Form1
Dim a As Integer
Public Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim prompt1, title1 As String
prompt1 = "Enter First Number : "
title1 = "First Number"
a = InputBox(prompt1, title1)
End Sub
Now you can use variable 'a'