I tried the example your directed me to and it worked, but the generated numbers are not starting like 001, 002

see code

        protected void LinkButton1_Click(object sender, EventArgs e)
        {
            Response.Redirect("Customer_Search.aspx");
        }

        protected void btncode_Click(object sender, EventArgs e)
        {
            string previousIdQuery = "SELECT MAX(Receipt) UniqueId FROM TransID";
            string newId = GenerateNewId(connStr, previousIdQuery);
            txtcode.Text = newId;
            string insertQuery = "INSERT INTO TransID VALUES(" + newId + ")";
            using (SqlConnection con = new SqlConnection(connStr))
            {
                con.Open();
                SqlCommand cmd = new SqlCommand(insertQuery, con);
                cmd.ExecuteNonQuery();
                con.Close();
            }
        }

        private string GenerateNewId(string connection, string query)
        {
            string newId = string.Empty;
            using (SqlConnection con = new SqlConnection(connection))
            {
                con.Open();
                SqlCommand cmd = new SqlCommand(query, con);
                SqlDataReader dr = cmd.ExecuteReader();
                while (dr.Read())
                {
                    string i = dr[0].ToString();
                    if (string.IsNullOrEmpty(i))
                    {
                        newId = "1";
                    }
                    else
                    {
                        int j = Convert.ToInt32(i);
                        j = j + 1;
                        newId = j.ToString();
                    }
                }
                con.Close();
            }

            return string.Concat(newId);
        }