extern "C" _declspec(dllexport) addValues(int a , int b)
{
  return (a + b);
}

    <System.Runtime.InteropServices.DllImport("MyDll.dll", _
    CallingConvention:=Runtime.InteropServices.CallingConvention.Cdecl, _
    EntryPoint:="addValues")> _
    Private Shared Function addValues(ByVal a As Integer, ByVal b As Integer) _
    As Integer
    End Function

 MessageBox.Show(Me.addValues(10, 10))

 Private Declare Auto Function addValues Lib "MyDll.dll" (ByVal a As Integer, _
   ByVal b As Integer) As Integer