跪求:VB.net加减乘除 代码

先在form上建立三个textbox，分别为textbox1,textbox2,textbox3，再建立四个按钮，分别为cmdplus,cmdminus,cmdmultiple,cmddivide，代码如下：
Private Sub cmdplus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdplus.Click
Dim a As Integer
Dim b As Integer
a = TextBox1.Text
b = TextBox2.Text
TextBox3.Text = a + b
End If

Private Sub cmdminus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdminus.Click
Dim a As Integer
Dim b As Integer
a = TextBox1.Text
b = TextBox2.Text
TextBox3.Text = a - b
End If
Private Sub cmdmultiple_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdmultiple.Click
Dim a As Integer
Dim b As Integer
a = TextBox1.Text
b = TextBox2.Text
TextBox3.Text = a * b
End If
P