ERROR:Conversion failed when converting the varchar value '311/3' to data type int.

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C#

Can any one tell me why it showing this error to me in this code

String SrNo = cSerialNo.Text;
          String SrNumber;
          string s = System.Configuration.ConfigurationSettings.AppSettings.Get("Conn");
          SqlConnection connection = new SqlConnection(s);
          connection.Open();
          SqlCommand cmd = new SqlCommand();
          cmd.Connection = connection;
          cmd.CommandText = ("SELECT c_SerialNo FROM Cultivator_tbl WHERE c_SerialNo=" +SrNo);
          SqlDataReader dr = cmd.ExecuteReader();
          DataTable dt = new DataTable();
          dt.Load(dr);//Error here
          cSerialNo.Text = dt.Rows[0][0].ToString();
          SrNumber = dt.Rows[0][0].ToString();
          if (SrNumber != "")
          {
              MessageBox.Show("SERIAL NO\t" + SrNumber + "\t ALREADY EXISTS");
          }
          connection.Close();

it showing me error for dt.Load(dr); line

ERROR:Conversion failed when converting the varchar value '311/3' to data type int.

I have define c_SerialNo as varchar(50) in my database.