C / C++ / MFC

int pnpoly(int nvert, float *vertx, float *verty, float testx, float testy)
{
  int i, j, c = 0;
  for (i = 0, j = nvert-1; i < nvert; j = i++) {
    if ( ((verty[i]>testy) != (verty[j]>testy)) &&
	 (testx < (vertx[j]-vertx[i]) * (testy-verty[i]) / (verty[j]-verty[i]) + vertx[i]) )
       c = !c;
  }
  return c;
}

Function pnpoly(ByVal nvert As Int16, ByVal vertx() As Decimal, ByVal verty() As Decimal, ByVal testx As Decimal, ByVal testy As Decimal) As Int16

  ' RETURNS:
  ' -1 IF THE POINT IS OUTSIDE OF THE POLYGON,
  '  0 IF THE POINT IS ON AN EDGE OR AT A VERTEX,
  '  1 IF THE POINT IS INSIDE OF THE POLYGON

    Dim i As Int16 = 0
    Dim j As Int16 = 0
    Dim c As Int16 = 0

    i = 0
    j = nvert - 1
    Do
        If Not ((verty(i) > testy) = (verty(j) > testy)) Then
            If testx < (vertx(j) - vertx(i)) * (testy - verty(i)) / (verty(j) - verty(i)) + vertx(i) Then
                c = Not c
            End If
        End If
        j = i
        i = i + 1
    Loop Until Not i < nvert
    pnpoly = c
End Function

Dim xcoor(7) As Decimal
Dim ycoor(7) As Decimal
xcoor(0) = 2
ycoor(0) = 2
xcoor(1) = 5
ycoor(1) = 1
xcoor(2) = 8
ycoor(2) = 2
xcoor(3) = 7
ycoor(3) = 4
xcoor(4) = 8
ycoor(4) = 6
xcoor(5) = 1
ycoor(5) = 7
x = pnpoly(6, xcoor, ycoor, 3, 3)