Private Sub TextBox1_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles TextBox1.KeyDown
If e.KeyCode = Keys.Enter Then
Dim rg As New Regex("\d+\s*(\+|\/|\*|\-)\s*\d+")
If Not rg.Match(TextBox1.Text).Success Then
MsgBox("invalid")
Else
Dim r() As String = Regex.Split(TextBox1.Text, "\s*[+,/,*,-]\s*")
If (Regex.Match(TextBox1.Text, "\s*\+\s*")).Success Then
TextBox1.Text = Integer.Parse(r(0)) + Integer.Parse(r(1))
ElseIf (Regex.Match(TextBox1.Text, "\s*\*\s*")).Success Then
TextBox1.Text = Integer.Parse(r(0)) + Integer.Parse(r(1))
ElseIf (Regex.Match(TextBox1.Text, "\s\/\s*")).Success Then
TextBox1.Text = Integer.Parse(r(0)) + Integer.Parse(r(1))
ElseIf (Regex.Match(TextBox1.Text, "\s*\-\s*")).Success Then
TextBox1.Text = Integer.Parse(r(0)) + Integer.Parse(r(1))
End If
End If
End If
end sub