How to generate the Autounique id

Question

  hi friends,

 

Iam develop the student Registration form  here student Click the Location in dropdown value  generate the  User Id  based on location  suppose

   student click Hyderbad  -------> userid = Hyd001

 student Click Hyderbad  -------> user id = Hyd002

student Click  chennai -----------> user id = che001  next  student click increment the value....

in the below iam writing the code where iam doing wrong please let me know....

protected void dpCity_SelectedIndexChanged(object sender, EventArgs e)
{

SqlConnection con = new SqlConnection("Data Source=SERVER;Initial Catalog=MuraliIIT;User ID=sa;Password=rits@1234");

string s = "select count(*) from NewStudentRegistrationForm where City ='" + dpCity.SelectedItem.Value + "'";
con.Open();
SqlCommand com = new SqlCommand(s, con);
int count = Convert.ToInt32(com.ExecuteScalar());
string city = dpCity.SelectedItem.Value;
string GeneratedId= "";
count+= 1;
if (count < 10)

GeneratedId = dpCity + "00" + count.ToString();

else if (count < 100)

GeneratedId = dpCity + "0" + count.ToString();

else

GeneratedId = dpCity + count.ToString();

TxtUserid.Text=GeneratedId;




}