title: How to save the result of a SQL query in a variable in C#.net?
body: <pre><code>namespace Hotel
  {
      public partial class Billing : Form
      {
          SqlConnection con = new SqlConnection();
          SqlDataAdapter da;
          SqlCommand cmd = new SqlCommand();
          DataTable dt = new DataTable();
          public Billing()
          {
              InitializeComponent();
          }
  
          private void Billing_Load(object sender, EventArgs e)
          {
              con.ConnectionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename=D:\\Projects\\c# assignments\\Hotel Manager\\Hotel\\database\\master.mdf;Integrated Security=True;User Instance=True";
              //loadData();
          }
  
          private void button1_Click(object sender, EventArgs e)
          {
              con.Open();
              int rno = Int32.Parse(txtRoom.Text);
  
  
              cmd.CommandText = "SELECT SUM(ItemRate) FROM logs WHERE RoomNo=" + rno +"";
              int amt = (int)cmd.ExecuteScalar();   //arror is at this part
  
         //ExecuteScalar: Connection property has not been initialized.
  
              cmd.CommandText = "INSERT INTO bill VALUES('" + txtBillNo.Text.ToString() + "','" + txtRoom.Text.ToString() + "','" + amt.ToString() + "')";
              con.Close();
              txtBillNo.Text = "";
              txtRoom.Text = "";
              BillView bv = new BillView();
              bv.ShowDialog();
          }
      }
  }
  </code></pre>
  
  <p>please help me with this error i am not able to store the the SQL query result into a variable???</p>