What is ToString("N0") format?

This code is from Charles Pettzold's "Programming Windows Sixth Edition" book:

public object Convert(object value, Type targetType, object parameter, string language) 
{ 
    return ((double)value).ToString("N0"); 
}

ToString("N0") is supposed to print the value with comma separators and no decimal points. I cannot find the reference to appropriate ToString overload and "N0" format in the documentation. Please point me to the right place in .NET documentation.

Checkout the following article on MSDN about examples of the N format. This is also covered in the Standard Numeric Format Strings article.

Relevant excerpts:

//       Formatting of 1054.32179:
//          N:                     1,054.32 
//          N0:                    1,054 
//          N1:                    1,054.3 
//          N2:                    1,054.32 
//          N3:                    1,054.322 

> When precision specifier controls the number of fractional digits in the result string, the result string reflects a number that is rounded to a representable result nearest to the infinitely precise result. If there are two equally near representable results: > > - On the .NET Framework and .NET Core up to .NET Core 2.0, the runtime selects the result with the greater least significant digit (that is, using MidpointRounding.AwayFromZero). > - On .NET Core 2.1 and later, the runtime selects the result with an even least significant digit (that is, using MidpointRounding.ToEven).

This is where the documentation is:

http://msdn.microsoft.com/en-us/library/dwhawy9k.aspx

> The numeric ("N") format specifier converts a number to a string of > the form "-d,ddd,ddd.ddd…", where "-" indicates a negative number > symbol if required, "d" indicates a digit (0-9) ...

And this is where they talk about the default (2):

http://msdn.microsoft.com/en-us/library/system.globalization.numberformatinfo.numberdecimaldigits.aspx

      // Displays a negative value with the default number of decimal digits (2).
      Int64 myInt = -1234;
      Console.WriteLine( myInt.ToString( "N", nfi ) );

Here is a good start maybe

Double.ToString()

Have a look in the examples for a number of different formating options Double.ToString(string)

You can find the list of formats here (in the Double.ToString()-MSDN-Article) as comments in the example section.

It is a sort of format specifier for formatting numeric results. There are additional specifiers on the link.

What N does is that it separates numbers into thousand decimal places according to your CultureInfo and represents only 2 decimal digits in floating part as is N2 by rounding right-most digit if necessary.

N0 does not represent any decimal place but rounding is applied to it.

Let's exemplify.

using System;
using System.Globalization;


namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            double x = 567892.98789;
            CultureInfo someCulture = new CultureInfo("da-DK", false);

            // 10 means left-padded = right-alignment
            Console.WriteLine(String.Format(someCulture, "{0:N} denmark", x));
            Console.WriteLine("{0,10:N} us", x); 

            // watch out rounding 567,893
            Console.WriteLine(String.Format(someCulture, "{0,10:N0}", x)); 
            Console.WriteLine("{0,10:N0}", x);

            Console.WriteLine(String.Format(someCulture, "{0,10:N5}", x));
            Console.WriteLine("{0,10:N5}", x);


            Console.ReadKey();

        }
    }
}

It yields,

567.892,99 denmark
567,892.99 us
   567.893
   567,893
567.892,98789
567,892.98789