Consuming a geoprocessing custom model in .NET
Program.cs
// Copyright 2012 ESRI
// 
// All rights reserved under the copyright laws of the United States
// and applicable international laws, treaties, and conventions.
// 
// You may freely redistribute and use this sample code, with or
// without modification, provided you include the original copyright
// notice and use restrictions.
// 
// See the use restrictions.
// 

using System;
using ESRI.ArcGIS.esriSystem;
using ESRI.ArcGIS.Geoprocessing;

namespace GeoprocessingInDotNet2008
{
    class Program
    {
        private static LicenseInitializer m_AOLicenseInitializer = new GeoprocessingInDotNet2008.LicenseInitializer();
    
        [STAThread()]
        static void Main(string[] args)
        {
            // Load the product code and version to the version manager
            ESRI.ArcGIS.RuntimeManager.Bind(ESRI.ArcGIS.ProductCode.Desktop);

            //ESRI License Initializer generated code.
            m_AOLicenseInitializer.InitializeApplication(new esriLicenseProductCode[] { esriLicenseProductCode.esriLicenseProductCodeAdvanced },
            new esriLicenseExtensionCode[] { });

            // Create geoprocessor. Overwrite true will replace existing output
            IGeoProcessor2 gp = new GeoProcessorClass();
            gp.OverwriteOutput = true;

            // Get the workspace from the user
            Console.WriteLine("Enter the path to folder where you copied the data folder.");
            Console.WriteLine("Example: C:\\AirportsAndGolf\\data");
            Console.Write(">");
            string wks = Console.ReadLine();

            // set the workspace to the value user entered
            gp.SetEnvironmentValue("workspace", wks + "\\" + "golf.gdb");

            // Add the custom toolbox to geoprocessor
            gp.AddToolbox(wks + "\\" + "Find Golf Courses.tbx");

            // Create a variant - data are in the workspace
            IVariantArray parameters = new VarArrayClass();
            parameters.Add("Airports");
            parameters.Add("8 Miles");
            parameters.Add("Golf");
            parameters.Add("GolfNearAirports");

            object sev = null;

            try
            {
                gp.Execute("GolfFinder", parameters, null);
                Console.WriteLine(gp.GetMessages(ref sev));
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                string errorMsgs = gp.GetMessages(ref sev);
                Console.WriteLine(errorMsgs);
            }
            finally
            {
                Console.WriteLine("Hit Enter to quit");
                Console.ReadLine(); // pause the console to see messages
            }

            //ESRI License Initializer generated code.
            //Do not make any call to ArcObjects after ShutDownApplication()
            m_AOLicenseInitializer.ShutdownApplication();
        }
    }
}