Dim a As Double
a = Val(Form1.Text1.Text)

Private Sub Command1_Click()
Text2.Visible = True
Text2.Text = Fix(a)
End Sub

Private Sub Command2_Click()
Text2.Visible = True
Text2.Text = Int(a)
End Sub

Private Sub Command3_Click()
Text2.Visible = True
Text2.Text = Abs(a)
End Sub

Private Sub Command4_Click()
Text2.Visible = True
Text2.Text = Sgn(a)
End Sub

Private Sub Command5_Click()
Text2.Visible = True
Text2.Text = Sqr(a)
End Sub

Private Sub Command6_Click()
Text2.Visible = True
Text2.Text = Exp(a)
End Sub

Private Sub Form_Load()
Text1.Text = ""
Text2.Text = ""
Text2.Visible = False
Command1.Caption = "fix(x)"
Command2.Caption = "int(x)"
Command3.Caption = "abs(x)"
Command4.Caption = "sgn(x)"
Command5.Caption = "sqr(x)"
Command6.Caption = "exp(x)"
End Sub
------------------------------------------
a = Val(Form1.Text1.Text) 插到每个单击事件中就有用了  。就不知道为什么 “模块的通用声明段”

VB 的程序结构是搭积木。
每个函数或过程，就是每一块积木。

你这句 a = Val(Form1.Text1.Text)  是一条可执行语句，就必须放到积木里执行。
当你放到积木外执行时，自然出错。

在积木外，只能在 变量 的定义 。

感谢 版主，我明白了  。