Complete Solution

complete-projects.cs

using System;
using System.ComponentModel;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using Microsoft.SharePoint;
using Microsoft.SharePoint.WebControls;

namespace SharePoint_webpart.Projects
{
    [ToolboxItemAttribute(false)]
    public class Projects : WebPart
    {
        //declare all variables

        TextBox txtproject;
        Button btnadd;

        //load all controls
        protected override void CreateChildControls()
        {
            txtproject = new TextBox();
            txtproject.ID = "txtproject";
            btnadd = new Button();
            btnadd.ID = "btnadd";
            btnadd.Text = "Add Project";
            btnadd.Click += btnadd_Click;
            Controls.Add(txtproject);
            Controls.Add(btnadd);
        }

        //Add the project to a list
        void btnadd_Click(object sender, EventArgs e)
        {
            SPWeb web = SPContext.Current.Web;
            //SPList projectsList = web.Lists["Projects"];
            //use the below line code for best prectices
            SPList projectsList = web.GetList("http://sharepoint-journey/sites/Apps/Lists/Projects/AllItems.aspx");
            SPListItem newItem = projectsList.Items.Add();
            newItem["Title"] = txtproject.Text.ToString();
            newItem.Update();
            txtproject.Text = string.Empty;
        }
    }
}