C / C++ / MFC

double /*__stdcall*/ square_in_C(double &arg) {return (arg*arg);}

Declare Function square_in_C _
Lib "C:/PATHTOFILE/debug/MyXLib.dll" (arg As Double) As Double

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Xml.Linq;

namespace WebServiceExample
{
    /// <summary>
    /// Summary description for Service1
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [ToolboxItem(false)]
    // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
    // [System.Web.Script.Services.ScriptService]
    public class Service1 : System.Web.Services.WebService
    {

        [WebMethod]
        public string HelloWorld()
        {
            return "Hello World";
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace MyClient
{
    class Program
    {
        [STAThread]
        static void Main(string[] args)
        {
            // Make an instance of the WebService Class
            // using the Web Reference you provided
            MyService.Service1 service = new MyService.Service1();
            // Assign message what ever is returned
            // from HelloWorld in this case "HelloWorld"
            string message = service.HelloWorld();
            // Prints out the message on the screen
            Console.WriteLine(message); 
        }
    }
}