DAL/DBHelper.cs

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data .SqlClient ;
using System.Data;



namespace DAL
{
   public class DBHelper
    {
       public DBHelper()
       { 
       
       }
       private static SqlConnection connection;
       public static SqlConnection Connection
       {
         get
         {
             connection =new SqlConnection ();
             connection .ConnectionString =System .Configuration .ConfigurationManager .ConnectionStrings ["connstr"].ConnectionString ;
             return DBHelper .connection ;
         }
       }
       public static DataTable GetTable(string strsql)
       {
           SqlConnection conn = connection ;
           SqlCommand cmd = new SqlCommand();
           cmd.Connection = conn;
           cmd.CommandText = strsql;
           DataTable dt = new DataTable();
           SqlDataAdapter daap = new SqlDataAdapter();
           daap.SelectCommand = cmd;
           daap.Fill(dt);
           return dt;
       }

       public static bool checkNo(string stuno)
       {
           bool flag = false;
           SqlConnection conn = connection ;
           SqlCommand cmd = new SqlCommand();
           cmd.Connection = conn;
           cmd.CommandText = "select count(*) from student where sno='"+stuno +"'";
           try
           {
               conn.Open();
               int n = (int)cmd.ExecuteScalar();
               if (n > 0)
               {
                   flag = true;
               }      


           }
           catch (Exception ex)
           {