求大神指导，跪谢！

楼上的没有考虑过阶乘的内存溢出问题吗？

这个问题应该先动笔，把式子化简一下，直接阶乘，无法计算。

仅供参考,以下代码不代表正确性.
private function jiecheng(x as double) as double
if (x=0 or x=1) then
jiecheng=1
exit function
else
jiecheng=x*jiecheng(x-1)
end if
end function
private sub command1_click()'要吃饭了简单凑合,自己搞.
text1=jiecheng(30)-jiecheng(28)-jiecheng(26)....-jiecheng(2)
end sub

先用function算出阶乘，再就简单了

function写好了，你调用就可以了！
Function jiecheng(n As Integer) As Integer
c = 1
For i = 1 To n
c = c * n
Next
jiecheng = c
End Function

Dim c As Long
c = jiecheng(30)
MsgBox c
这已经溢出了

@骄傲地蚂蚁 @happy丶2b青年 @cushaw80
看一看这个，不是我原创的，但是速度还是比较快，计算1000位的阶乘：1000！
Function multi(ByVal X As String, ByVal Y As String) As String 'multi of two huge hexnum（两个大数之积）
Dim result As Variant
Dim xl As Long, yl As Long, temp As Long, i As Long
xl = Len(Trim(X))
yl = Len(Trim(Y))
ReDim result(1 To xl + yl)
For i = 1 To xl
For temp = 1 To yl
result(i + temp) = result(i + temp) + Val(Mid(X, i, 1)) * Val(Mid(Y, temp, 1))
Next
Next
For i = xl + yl To 2 Step -1
temp = result(i) \ 10
result(i) = result(i) Mod 10
result(i - 1) = result(i - 1) + temp
Next
If result(1) = "0" Then result(1) = ""
multi = Join(result, "")
Erase result
End Function
Private Sub Command1_Click() '节约时间，算到1000！
For i = 1 To 9
calcfactorial i * 100
Next
End Sub
Sub calcfactorial(ByVal n As Integer)
Dim a() As String, i As Long, stimer As Double
ReDim a(1 To n)
a(1) = 1
stimer = Timer
For i = 2 To n
a(i) = multi(a(i - 1), i)
Next
Debug.Print n & "！ ： 用时 "; Timer - stimer & " 秒, 结果 " & Len(a(n)) & " 位"
Debug.Print a(n)
End Sub