Visual Basic中的For-Next循环

Question

我想在Visual basic中计算二项式系数，但我只能计算分子部分，因为我不知道分母部分。我使用的方程式如下图所示。

Equations

看看C(n，k)方程，我只能做n阶乘的分子。我在分母方面遇到了问题。我的分子代码(n!)如下所示：

Dim nfactorial As Integer = 1
    For i As Integer = 1 To txt3.Text
       nfactorial *= i
    Next

我应该如何处理分母部分？谢谢!

Answer 1

不能分别计算分子和分母。你有没有试着找(30!)在.NET中，尤其是在Integer中？这是家庭作业吗？无论如何，只要看一下下面的帖子：http://csharphelper.com/blog/2014/08/calculate-the-binomial-coefficient-n-choose-k-efficiently-in-c/

vb中的代码：

Dim result As Decimal = 1
For i As Integer = 1 To K
    result *= N - (K - i)
    result /= i
Next
Return result

Answer 2

试试这个：

'by example: C(5,3) = 10
Dim n, k As Integer
Dim result As String = ""
n = txt3.Text
For k = 0 To 3
    result = result & "For C(" & n & "," & k & ")=" & C(n, k) & vbCrLf
Next
MsgBox(result)
.  
.
.

Private Function C(n As Integer, k As Integer)
    Dim result As Decimal = 1
    For i As Integer = 1 To k
        result *= n - (k - i)
        result /= i
    Next
    Return result
End Function

编辑：用于键盘输入的k=0 to 3和n。