“Input string was not in a correct format” when parsing numbers [duplicate]

Answer 1

I searched on google the 'System.FormatException' and this link seemed useful this link

Here it says that "You can't convert a null value to a meaningful value through Convert. Your best option is to check for null first and then assign a value of 0 (or whatever) to the result (whereever Convert was sending its results too)."

You can check of null or you can try this:

  int NoOfRooms ;
  bool result = Int32.TryParse(txtNoRooms.Text, out NoOfRooms);

Here result will be true if the conversion was finalized successfully and false otherwise. And the same for the double value. You can then use the Boolean values in order to determine if the conversion finished successfully and take some actions accordingly.

Answer 2

Given that your table was pretty simple and it seemed odd that it didn't work I thought I'd try it out myself. Below is what I came up with:

var roomCost = 100.0; // whatever the room cost based on the room type
// You should probably use try parse
var RoomType = string.IsNullOrEmpty(txtRoomType.Text) ? 1 : Convert.ToInt32(txtRoomType.Text.Trim());
var NoOfRooms = string.IsNullOrEmpty(txtNoOfRooms.Text) ? 1 : Convert.ToInt32(txtNoOfRooms.Text.Trim());
var NoOfNights = string.IsNullOrEmpty(txtNoOfNights.Text) ? 1 : Convert.ToInt32(txtNoOfNights.Text.Trim());
var totalCostHotel = (roomCost * NoOfRooms) * NoOfNights;
// you will need to change the connection string to what you need
var connectionString = "server=localhost;database=testdb;Integrated Security=true;";
using (SqlConnection connection = new SqlConnection(connectionString))
{
    var queryString = new StringBuilder();
    queryString.AppendLine("INSERT INTO [dbo].[HotelData]");
    queryString.AppendLine("([RoomType],[NoOfRooms],[NoOfNights],[totalCostHotel])");
    queryString.AppendLine("VALUES (@RoomType, @NoOfRooms, @NoOfNights, @totalCostHotel)");
    try
    {
        SqlCommand command = new SqlCommand(queryString.ToString(), connection);
        command.Connection.Open();
        command.Parameters.AddWithValue("@RoomType", RoomType);
        command.Parameters.AddWithValue("@NoOfRooms", NoOfRooms);
        command.Parameters.AddWithValue("@NoOfNights", NoOfNights);
        command.Parameters.AddWithValue("@totalCostHotel", totalCostHotel);
        command.ExecuteNonQuery();
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
    }
}

Consider using a Stored Procedure

Instead of writing the INSERT statement directly, I tend to use a SP to insert/update