private void Form1_Load(object sender, EventArgs e)

        {

            AutoCompleteStringCollection source = new AutoCompleteStringCollection();

            source.AddRange(new string[]

                    {

                        "January",

                        "February",

                        "March",

                        "April",

                        "May",

                        "June",

                        "July",

                        "August",

                        "September",

                        "October",

                        "November",

                        "December"

                    });  

            TextBox textBox = new TextBox();  

            textBox.AutoCompleteCustomSource = source;

            textBox.AutoCompleteMode =

                AutoCompleteMode.SuggestAppend;

            textBox.AutoCompleteSource =

                AutoCompleteSource.CustomSource;

            textBox.Location = new Point(20, 20);

            textBox.Width = ClientRectangle.Width - 40;

            textBox.Visible = true;  

            Controls.Add(textBox);

            //comboBox1.DropDownHeight = 300;  

        }