How to call a fortran in vc++ and callback c function

Hi!  I create a fortran dll that it can pass an array to sum its elements and call a c function below:

module callctest

    use, intrinsic :: iso_c_binding

    implicit none
    private
    public callcfun

    contains

    subroutine callcfun(a,b) bind(C,name = "callcfun")
    !DEC$ ATTRIBUTES DLLEXPORT :: callcfun
        implicit none

        real(c_double), dimension(*):: a !receive an array from c
        type(c_funptr), value :: b ! receive a c function

        real,  parameter::pi=3.14159
        integer :: i
        real :: sum = 0.0

        do i = 1,3          ! sum the array elements
            sum = sum+a(i)
        end do
        write(*,*) 'total',sum
        return

    end subroutine callcfun

    end module callctest

And c code that it call fortran with passing c function that it print words and an input integer:

#include "stdafx.h"
    #include <iostream>

    using namespace std;

    extern "C" {

    	void callcfun( double[], void(f)(int)); //

    }

    void sayhello(int a){


    	cout << "Hi! fortran "<<a<< endl;
    }
    int main(){

    	double a[] = { 10.0, 50, 3.0 };

    	callcfun(a, sayhello(50));

    	system("pause");
    	return 0;

    }

But the problem in function sayhello(50). Error list shows: 

Error    1    error C2664: 'void callcfun(double [],void (__cdecl *)(int))' : cannot convert argument 2 from 'void' to 'void (__cdecl *)(int)'  

IntelliSense: argument of type "void" is incompatible with parameter of type "void (*)(int b)" 

 How to solve it? Thanks!