Where is the problem?

[Jonno12345]

I am trying to make it so that the text in 4 textboxes are added to the last row of a table, and thought of this:

Private Sub CommandButton1_Click()
ColumnA = Range("A4:A1000")
For Each c In ColumnA
    If c = "" Then
        c = TextBox1.Text
        Exit For
    End If
Next c
For Each c In Range("B4:B1000")
    If c = "" Then
        c = TextBox2.Text
        Exit For
    End If
Next c
For Each c In Range("C4:C1000")
    If c = "" Then
        c = TextBox3.Text
        Exit For
    End If
Next c
For Each c In Range("A4:A1000")
    If c = "" Then
        c = TextBox4.Text
        Exit For
    End If
Next c
End Sub

However it does absolutely nothing. Any ideas?