Calling a Function from Fortran DLL with Excel VBA

Hello, Everyone.

I am a newbie to VBA calling Fortran DLL.

I need some help getting my Fortran DLL file to work with my Excel VBA. 

I am using Windows 7 (X64), Excel 2013 (X64), Microsoft Visual Studio 2015 and  Visual Fortran Composer XE 2013 SP1.

【My FORTRAN code】

Function IntelRho(pi,ti)
    !DEC$ ATTRIBUTES STDCALL,DLLEXPORT::IntelRho
    !DEC$ ATTRIBUTES ALIAS:'IntelRho'::IntelRho
    implicit real(8) (A-H,O-Z)
    real(8) pi,ti,p,t,Intelrho
    p=pi*1000
    t=ti + 273.15
    IntelRho=p/(8.31*t)
    return
End Function Intelrho

【My VBA code】

Public Declare PtrSafe Function Intelrho Lib "D:\Doc\VS2015\Dll2IntelRho\x64\Debug\Dll2IntelRho.dll" (pp As Double, tt As Double) As Double

----------------------------------------------------------------------------------------------------------

When I call the function in an Excel cell, such as: I put 3 in Cells(1,1), put 10 in Cells(1,2), then I call the function IntelRho in Cells(1,3) as "=IntelRho(A1,B1)", I got a wrong answer(Cells(1,3)=0). Could anyone tell what the problem is?

Any help is appricated.

Guo