using System;

using System.Runtime.InteropServices;

namespace zzzili

{

    class Test{

        [DllImport("dllTest.dll")]

        public static extern int MyDll_Add(int a, int b);               

        static void Main()

        {

           Console.WriteLine(MyDll_Add(1,2).ToString());

        }

    }

}

dllTest.C

extern "C"  __declspec(dllexport) int MyDll_Add(int a,int b);

int MyDll_Add(int a,int b)

{

 return a+b;

}