Visual basic express 2008 help

This is my 2 step math equation solver:

Public Class Form1
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        TextBox2.Text = "x"
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        If ComboBox1.Text = "+" Then
            Dim a
            Dim b
            Dim c
            Dim d
            a = TextBox1.Text
            b = TextBox3.Text
            c = TextBox4.Text
            d = c - b
            MsgBox(d / a)
        Else
        End If
        If ComboBox1.Text = "-" Then
            Dim n
            Dim f
            Dim g
            Dim h
            n = TextBox1.Text
            f = TextBox3.Text
            g = TextBox4.Text
            h = g + f
            MsgBox(h / n)
        End If
    End Sub
End Class

Code (markup):

When i use the subtraction sign, i get a wrong answer. why is this?

 

For a start lets do some basic cleaning up:

  Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim a As Single = Single.Parse(TextBox1.Text)
        Dim b As Single = Single.Parse(TextBox3.Text)
        Dim c As Single = Single.Parse(TextBox4.Text)
        Dim result As Single

        If ComboBox1.Text = "+" Then
            result = (c - b)/a
        Else If ComboBox1.Text = "-" Then
            result = (c + b)/a
        End If
        
        MsgBox(result.toString)

    End Sub

Code (markup):

Can you explain whats meant to be going on? Because "-" doesn't mean "(c + b)/a" to me, it usually means a-b=c.

 

in the equation, lets say it is 2x-6=4.
you would add the 6 to both sides.
this would give you 2x = 10
then you divide both sides by 2
answer = 6

a=2 b=6 c=4

 

Cool, that makes sense.

The question now is, what is the error that your complaining about?

 

It works now, but when I was using it with the subtraction sign, it would just add the two numbers as in putting them next to each other
ex
1x - 2 = 2
answer would be 22 and idk why