我用VB编了一个开方的程序，但是一直运行不了，每次运行时都提示“子程序或函数未定义”请问高手问题在哪里？现把程序附上：
Private Sub form_click()

Dim a As Single, b As Single, c As Single, n As Integer
n = 0
a = 3
c = 1.5
pp
b = (c + a / c) / 2
n = n + 1
If (Abs(b - c) > e - 5)
c = b
GoTo pp
Print "b="; b
Print "n="; n
End Sub