SharePoint : How can I programmatically add items to a custom list instance

I think these both blog post should help you solving your problem.

http://blog.the-dargans.co.uk/2007/04/programmatically-adding-items-to.html http://asadewa.wordpress.com/2007/11/19/adding-a-custom-content-type-specific-item-on-a-sharepoint-list/

Short walk through:

1. Get a instance of the list you want to add the item to.

2. Add a new item to the list:

   SPListItem newItem = list.AddItem();
   

3. To bind you new item to a content type you have to set the content type id for the new item:

   newItem["ContentTypeId"] = <Id of the content type>;
   

4. Set the fields specified within your content type.

5. Commit your changes:

   newItem.Update();
   

To put it simple you will need to follow the step.

1. You need to reference the Microsoft.SharePoint.dll to the application.

2. Assuming the List Name is Test and it has only one Field "Title" here is the code.

           using (SPSite oSite=new SPSite("http://mysharepoint"))
       {
           using (SPWeb oWeb=oSite.RootWeb)
           {
               SPList oList = oWeb.Lists["Test"];
               SPListItem oSPListItem = oList.Items.Add();
               oSPListItem["Title"] = "Hello SharePoint";
               oSPListItem.Update();
           }
   
       }
   

3. Note that you need to run this application in the Same server where the SharePoint is installed.

4. You dont need to create a Custom Class for Custom Content Type

This is how it was on the Microsoft site, with me just tweaking the SPSite and SPWeb since these might vary from environment to environment and it helps not to have to hard-code these:

using (SPSite oSiteCollection = new SPSite(SPContext.Current.Site.Url))
{
    using (SPWeb oWeb = oSiteCollection.OpenWeb(SPContext.Current.Web))
    {
        SPList oList = oWeb.Lists["Announcements"];
        // You may also use 
        // SPList oList = oWeb.GetList("/Lists/Announcements");
        // to avoid querying all of the sites' lists
        SPListItem oListItem = oList.Items.Add();
        oListItem["Title"] = "My Item";
        oListItem["Created"] = new DateTime(2004, 1, 23);
        oListItem["Modified"] = new DateTime(2005, 10, 1);
        oListItem["Author"] = 3;
        oListItem["Editor"] = 3;
        oListItem.Update();
    }
}

Source: SPListItemClass (Microsoft.SharePoint). (2012). Retrieved February 22, 2012, from http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.splistitem.aspx.

You can create an item in your custom SharePoint list doing something like this:

using (SPSite site = new SPSite("http://sharepoint"))
{
    using (SPWeb web = site.RootWeb)
    {
        SPList list = web.Lists["My List"];
        SPListItem listItem = list.AddItem();
        listItem["Title"] = "The Title";
        listItem["CustomColumn"] = "I am custom";
        listItem.Update();
     }
}

Using list.AddItem() should save the lists items being enumerated.