vb编程题:n!/(m!*(n-m)!). 怎么编写

先编一个阶乘函数：
Function Factorial(ByVal n As Integer) As Long
If n < 0 Then
Factorial = 0 '小于0则得0
Else
Factorial = 1
For i = 1 To n
Factorial = Factorial * i
Next
End If
End Function

输入n,m后，只要代入就行了。
r=Factorial(n)/(Factorial(m)*Factorial(n-m))