código c#

        [DllImport("NewDll.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern double soma(double a, double b);

        [DllImport("NewDll.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
        public static extern string mensagem(string x);

        [DllImport("NewDll.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern double subtracao(double a, double b);