Oddity with ToString() custom number formatting

Question

I am trying to convert numbers in the form 123456 to 123,456 which I find easy enough by using the .NET ToString() method with a custom format of N0.

However in one case of data I am getting strange formats whilst using this method.

In this case I am generating a DataTable dynamically for my input table to test the code.

DataTable dt = new DataTable();

dt.Columns.Add("Cases", typeof(Int32));

For example my data looks like this before formatting is applied.

--------------------------------------------
| Cases | 2495 | 3937 | 3207 | 4173 | 4265 |
--------------------------------------------

I would like it to look like this.

-------------------------------------------------
| Cases | 2,495 | 3,937 | 3,207 | 4,173 | 4,265 |
-------------------------------------------------

I try formatting it by using code like so.

output.Rows[r][c] = Convert.ToInt32(input.Rows[c - 1][r + 1]).ToString("N0");

(Note: The reason for the strange formatting is because I am taking a DataTable and transposing it to another DataTable.)

Using the above formatting I now get the following data returned.

--------------------------------------------------------------------------
| Cases | 01/02/0495 | 01/03/0937 | 01/03/0207 | 01/04/0173 | 01/04/0265 |
--------------------------------------------------------------------------

I then tried it with one decimal point using:

output.Rows[r][c] = Convert.ToInt32(input.Rows[c - 1][r + 1]).ToString("N01");

Which gave me the following result.

------------------------------------------------------
| Cases | 2495.0 | 3937.0 | 3207.0 | 4173.0 | 4265.0 |
------------------------------------------------------

This has now confused me because it is accepting the fact that the number can be formatted this way.

The next thing I tried was different ways of formatting strings like so.

output.Rows[r][c] = string.Format("{0:N0}", input.Rows[c - 1][r + 1]);
output.Rows[r][c] = Convert.ToInt32(input.Rows[c - 1][r + 1]).ToString("#,##0");

None of these give the number format how I would like either. Can anybody advise where I am going wrong? Is it so simple that I have missed the point?

Answer 1

It looks to me simply that you've set the data-type of the columns in the DataTable incorrectly. Try making it explicit as an int (it looks like DateTime at the moment).

Also - the job of the DataTable is to hold data; not to disply it. You could store it pre-formatted as strings, I guess (as long as you tell it that the columns are strings) - but if you are storing it as int, then forget the display; as soon as you have run Convert.ToInt32 your job is over. How it appears is the job of the DataGridView (or whatever); tell that about "N0"...

Answer 2

Try using simply "N" as in ToString("N");