vb计时器的设计

设计一个计时器，一个text,两个command按钮，单击”开始计时“按钮，计时器按”时：分：秒“的形式开始计时，并显示在文本框中，此时开始计时，按钮变成”停止计时“按钮，停止计时，单击”清零”按钮，清除文本框内的时间。请问这个程序该怎么设计

新建一个文本框，两个按钮，一个时间控件

然后打开代码框 把里面的代码全清空，再把下面的复制进去就可以了
Dim a, b, c, d As Integer

Private Sub Command1_Click()

If Command1.Caption = "开始计时" Then

Timer1.Enabled = True
Timer1.Interval = 100

Command1.Caption = "停止计时"
Else

Timer1.Enabled = False
Timer1.Interval = 0
Command1.Caption = "开始计时"
End If
End Sub

Private Sub Command2_Click()
a = 0
b = 0
c = 0
d = 0
Text1.Text = a & ":" & b & ":" & c & ":" & d

Timer1.Enabled = False
Timer1.Interval = 0

End Sub

Private Sub Form_Load()

a = 0
b = 0
c = 0
d = 0
Text1.Text = a & ":" & b & ":" & c & ":" & d

Command1.Caption = "开始计时"
Command2.Caption = "清零"
Timer1.Enabled = False
Timer1.Interval = 0

End Sub