VERSION 5.00
Begin VB.Form Form1 
   Caption         =   "Form1"
   ClientHeight    =   4890
   ClientLeft      =   60
   ClientTop       =   345
   ClientWidth     =   4680
   LinkTopic       =   "Form1"
   ScaleHeight     =   4890
   ScaleWidth      =   4680
   StartUpPosition =   3  'Windows Default
   Begin VB.CommandButton Command1 
      Caption         =   "Command1"
      Height          =   375
      Left            =   2880
      TabIndex        =   0
      Top             =   4080
      Width           =   1335
   End
End
Attribute VB_Name = "Form1"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
Private Sub Command1_Click()
    'PROGRAM D4R2
    'Driver for routine FACTRL
    Open "D:\VB常用數值算法集\DATA\FNCVAL.DAT" For Input As #1
    Do
      Line Input #1, Text$
    Loop While Text$ <> "N-factorial"
    Line Input #1, NVAL$
    NVAL = Val(NVAL$)
    Print Text$
    Print
    Print "   N         Actual             FACVAL(N)"
    For I = 1 To NVAL
        Line Input #1, DUM$
        N = Val(Mid(DUM$, 1, 2))
        ACTUAL = Val(Mid(DUM$, 8))
        If ACTUAL < 10000000000# Then
            Print Tab(4); Format$(N, "##0");
            Print Tab(14); Format$(ACTUAL, "#########.");
            Print Tab(33); Format$(FACTRL(N), "########.")
        Else
            Print Tab(4); Format$(N, "##0");
            Print Tab(14); Format$(ACTUAL, ".######0E+00");
            Print Tab(33); Format$(FACTRL(N), ".######0E+00")
        End If
    Next I
    Close #1
End Sub
Function FACTRL(N)
    Dim A(33)
    NTOP = 0
    A(1) = 1#
    If N < 0 Then
        Print "negative factorial"
        Exit Function
    ElseIf N <= NTOP Then
        FACTRL = A(N + 1)
    ElseIf N <= 32 Then
        For J = NTOP + 1 To N
            A(J + 1) = J * A(J)
        Next J
        NTOP = N
        FACTRL = A(N + 1)
    Else
        FACTRL = Exp(GAMMLN(N + 1#))
    End If
End Function
Function GAMMLN(XX)
    Dim COF(6)
    COF(1) = 76.18009173
    COF(2) = -86.50532033
    COF(3) = 24.01409822
    COF(4) = -1.231739516
    COF(5) = 0.00120858003
    COF(6) = -0.00000536382
    STP = 2.50662827465
    HALF = 0.5
    ONE = 1#
    FPF = 5.5
    X = XX - ONE
    TMP = X + FPF
    TMP = (X + HALF) * Log(TMP) - TMP
    SER = ONE
    For J = 1 To 6
        X = X + ONE
        SER = SER + COF(J) / X
    Next J
    GAMMLN = TMP + Log(STP * SER)
End Function