how to auto increment a varchar column value in C#

First Add & then Delete the Record..

Actually I have a problem.....When a record is deleted and when a new record is inserted its ID is the same as the previous record...So please tell me what to do...????

Thank You Buddy......!!!

Can you please explain the code......???
what is lbl_castecode

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;
namespace Dynamic_generate_id
{
    public partial class Form1 : Form
    {
        string ConnectionString = System.Configuration.ConfigurationSettings.AppSettings["dsn"];
        OleDbCommand com;
        string str;
        int count;

        public Form1()
        {
            InitializeComponent();
        }

        private void btn_save_Click(object sender, EventArgs e)
        {
            OleDbConnection con = new OleDbConnection(ConnectionString);
            con.Open();
            str = "insert into caste(cast_code,cast_desc) values('" + lbl_castecode.Text.Trim() + "','" + txt_castename.Text.Trim() + "')";
            com = new OleDbCommand(str, con);
            com.ExecuteNonQuery();
            con.Close();
            MessageBox.Show("Records successfully Inserted");
            txt_castename.Text = "";
            autogenerated();
        }
       private void autogenerated()
        {
            OleDbConnection con = new OleDbConnection(ConnectionString);
            str = "select count(*) from caste";
            com = new OleDbCommand(str, con);
            con.Open();
            count =  Convert.ToInt16(com.ExecuteScalar()) + 1;
            lbl_castecode.Text = "P" + count.ToString();
            lbl_castecode.Enabled = false;
            con.Close();
        }

       private void Form1_Load(object sender, EventArgs e)
       {
           autogenerated();
       }
    }
}