如下是vc版FFT模板，能不能用？如何用？

void fft(cp *a,int n,int inv)
{
    int bit=0;
    while ((1<<bit)<n)bit++;
    fo(i,0,n-1)
    {
        rev[i]=(rev[i>>1]>>1)|((i&1)<<(bit-1));
        if (i<rev[i])swap(a[i],a[rev[i]]);//不加这条if会交换两次（就是没交换）
    }
    for (int mid=1;mid<n;mid*=2)//mid是准备合并序列的长度的二分之一
    {
        cp temp(cos(pi/mid),inv*sin(pi/mid));//单位根，pi的系数2已经约掉了
        for (int i=0;i<n;i+=mid*2)//mid*2是准备合并序列的长度，i是合并到了哪一位
        {
            cp omega(1,0);
            for (int j=0;j<mid;j++,omega*=temp)//只扫左半部分，得到右半部分的答案
            {
                cp x=a[i+j],y=omega*a[i+j+mid];
                a[i+j]=x+y,a[i+j+mid]=x-y;//这个就是蝴蝶变换什么的
            }
        }
    }
}

9楼的可调用程序如何调用？老提示参数类型不对或缺少定义？

希望各位老师和好朋友继续给予指导！非常感谢！

建议：
你把相关的数据代码放上，出错的提示，运算的数据（数组）。
没有相关数据，别人怎么测试，
傅立叶变换，听起来就是高大上的，因为别人没有用到，就不会去造数据的。

没有相关数据，我就是输入一个数值计算，结果是数据（数组）类型不符?我是这样用的：
x=fft("123456789")

非常感谢老师的指导和帮助！欢迎批评！
不知道怎么弄了，该怎么用?

代码如下：
Public Function fft(ByRef Data() As Double) As Double()
    ReDim ffft(128, 2) As Double
    Dim length As Integer
    length = UBound(Data, 1) + 1
'    Dim numArray(length - 1, 2) As Double
      
    Dim index As Integer
    Dim num5 As Integer
    Dim num6 As Integer
    Dim num7 As Integer
    Dim num10 As Integer
    Dim num3 As Integer
    Dim num2 As Integer
    Dim num11 As Integer
    Dim num9 As Integer
    num9 = length
      
    Dim num8 As Integer
    num8 = CInt(Math.Log(CDbl(num9)) / Math.Log(2#))
      
    Dim numArray2(128) As Double
    Dim numArray3(128) As Double
    Dim numArray4(128) As Double
    Dim numArray5(128) As Double
    For index = 0 To num9 - 1
        numArray2(index) = Data(index)
        numArray3(index) = 0#
    Next
    Dim a As Double
    Dim num14 As Double
      
   num14 = 6.28318530717959 / CDbl(num9)
    index = 0
    While index < (num9 \ 2)
        numArray4(index) = Math.Sin(a)
        numArray5(index) = Math.Cos(a)
        a = a + num14
        index = index + 1
    Wend
    num7 = num9
    num3 = 1
    For num2 = 1 To num8
        num7 = num7 / 2
        num6 = 0
        For num11 = 1 To num3
            num10 = 0
            index = num6
            While index <= ((num7 + num6) - 1)
                num5 = index + num7
                a = numArray2(index) - numArray2(num5)
                num14 = numArray3(index) - numArray3(num5)
                numArray2(index) = numArray2(index) + numArray2(num5)
                numArray3(index) = numArray3(index) + numArray3(num5)
                If num10 = 0 Then
                    numArray2(num5) = a
                    numArray3(num5) = num14
                Else
                    numArray2(num5) = (a * numArray5(num10)) + (num14 * numArray4(num10))
                    numArray3(num5) = (num14 * numArray5(num10)) - (a * numArray4(num10))
                End If
                num10 = num10 + num3
                index = index + 1
           Wend
            num6 = (num6 + num7) + num7
        Next
        num3 = num3 + num3
    Next
    num5 = num9 \ 2
    For index = 1 To (num9 - 1)
        num6 = num9
        If num5 < index Then
            Dim num12 As Double
              
          num12 = numArray2(index)
            numArray2(index) = numArray2(num5)
            numArray2(num5) = num12
            num12 = numArray3(index)
            numArray3(index) = numArray3(num5)
            numArray3(num5) = num12
        End If
        num6 = num6 / 2
        Do While num5 >= num6
            num5 = num5 - num6
            num6 = num6 / 2
            If num5 = 0 Then
                Exit Do
            End If
        Loop
        num5 = num5 + num6
    Next
    For index = 0 To num9 - 1
        numArray(index, 0) = numArray2(index)
        numArray(index, 1) = numArray3(index)
        numArray(index, 2) = ((numArray2(index)) ^ 2# + (numArray3(index)) ^ 2#) ^ 0.5
    Next
   fft = numArray
End Function

Private Sub Command1_Click()
Dim x
x = fft("123456789")
Text1 = x
End Sub

Private Sub Command2_Click()
Text1 = ""
End Sub

如下图片就是启动程序的结果：

fft()函数你定义的传递数据是数组，你把一个字符串传递过去，肯定出错的啊。

Function fft(ByRef Data() As Double) As Double()
返回的就是一个数，哪来的有虚部，实部数据呢？
到底是要算什么？

谢谢指导和帮助！
这个可调用程序是复制人家的，不知道这个数组如何调用？如何输入?
实部和虚部是人家的说明和提示。不知道，不明白程序的原理。