WHEN WE DEFINE DATATYPE THEN WRITE

employeeid IDENTITY(1,1)

try
            {
                string connStr = "Data Source=DEV1;Initial Catalog=SuperRental;Integrated Security=SSPI;";
                using (SqlConnection conn = new SqlConnection(connStr))
                {
                    conn.Open();
                    string sqlQuery = "INSERT INTO tbl_employee (EmployeeName) VALUES ('Sardar'); SELECT @@identity";
                    using (SqlCommand cmd = new SqlCommand(sqlQuery, conn))
                    {
                        object obj_employeeCode = cmd.ExecuteScalar();
                        int employeeCode = int.Parse(obj_employeeCode.ToString());

                        System.Console.WriteLine("New Employee code is : " + employeeCode);
                    }
                }
            }
            catch (Exception ex)
            {
                System.Console.WriteLine(ex.Message);
            }

You can do that easily by going into your datatable ,select the employee code column . On the column properties select Yes for the IsIdentity property .set the identity increament to the step you want each number to auto increament with . this way everytime you enter / create an employee entry the employee code auto increaments .

I do hope this helps.

con.open();
string r = "select max(substring(empid,5,5))from employee";
cmd=new sqlcommand(str,con);
sqldatareader dr;
dr=cmd.executenonquery();
int d = Convert.ToInt32(r);
int k = d + 1;

if (dr.Read() == true)

{
   
    textbox1.text="emp0"+k;
}
con.close();