.NET String.Format() to add commas in thousands place for a number

String.Format("{0:n}", 1234);  // Output: 1,234.00
String.Format("{0:n0}", 9876); // No digits after the decimal point. Output: 9,876

I found this to be the simplest way:

myInteger.ToString("N0")

int number = 1000000000;
string whatYouWant = number.ToString("#,##0");
//You get: 1,000,000,000

If you want culture specific, you might want to try this:

use namespace:"using System.Globalization;"

(19950000.0).ToString("N",new CultureInfo("en-US")) = 19,950,000.00

(19950000.0).ToString("N",new CultureInfo("is-IS")) = 19.950.000,00

Indian culture: (19950000.0).ToString("N",new CultureInfo("hi-IN"))= 1,99,50,000.00

Note: Some cultures use , to mean decimal rather than . so be careful.

Standard formats, with their related outputs,

Console.WriteLine("Standard Numeric Format Specifiers");
String s = String.Format("(C) Currency: . . . . . . . . {0:C}\n" +
                    "(D) Decimal:. . . . . . . . . {0:D}\n" +
                    "(E) Scientific: . . . . . . . {1:E}\n" +
                    "(F) Fixed point:. . . . . . . {1:F}\n" +
                    "(G) General:. . . . . . . . . {0:G}\n" +
                    "    (default):. . . . . . . . {0} (default = 'G')\n" +
                    "(N) Number: . . . . . . . . . {0:N}\n" +
                    "(P) Percent:. . . . . . . . . {1:P}\n" +
                    "(R) Round-trip: . . . . . . . {1:R}\n" +
                    "(X) Hexadecimal:. . . . . . . {0:X}\n",
                    - 1234, -1234.565F);
Console.WriteLine(s);

Example output (en-us culture):

(C) Currency: . . . . . . . . ($1,234.00)
(D) Decimal:. . . . . . . . . -1234
(E) Scientific: . . . . . . . -1.234565E+003
(F) Fixed point:. . . . . . . -1234.57
(G) General:. . . . . . . . . -1234
    (default):. . . . . . . . -1234 (default = 'G')
(N) Number: . . . . . . . . . -1,234.00
(P) Percent:. . . . . . . . . -123,456.50 %
(R) Round-trip: . . . . . . . -1234.565
(X) Hexadecimal:. . . . . . . FFFFFB2E

This is the best format. Works in all of those cases:

String.Format( "{0:#,##0.##}", 0 ); // 0
String.Format( "{0:#,##0.##}", 0.5 ); // 0.5 - some of the formats above fail here. 
String.Format( "{0:#,##0.##}", 12314 ); // 12,314
String.Format( "{0:#,##0.##}", 12314.23123 ); // 12,314.23
String.Format( "{0:#,##0.##}", 12314.2 ); // 12,314.2
String.Format( "{0:#,##0.##}", 1231412314.2 ); // 1,231,412,314.2

The most voted answer was great and has been helpful for about 7 years. With the introduction of C# 6.0 and specifically the String Interpolation there's a neater and, IMO safer, way to do what has been asked to add commas in thousands place for a number:

var i = 5222000;
var s = $"{i:n} is the number"; // results to > 5,222,000.00 is the number
s = $"{i:n0} has no decimal"; // results to > 5,222,000 has no decimal

Where the variable i is put in place of the placeholder (i.e. {0}). So there's no need to remember which object goes to which position. The formatting (i.e. :n) hasn't changed. For a complete feature of what's new, you may go to this page.

just simple as this:

float num = 23658; // for example 
num = num.ToString("N0"); // Returns 23,658

more info is in Here

String.Format("{0:#,###,###.##}", MyNumber)

That will give you commas at the relevant points.

The following example displays several values that are formatted by using custom format strings that include zero placeholders.

String.Format("{0:N1}", 29255.0);

Or

29255.0.ToString("N1")

result "29,255.0"

String.Format("{0:N2}", 29255.0);

Or

29255.0.ToString("N2")

result "29,255.00"

If you wish to force a "," separator regardless of culture (for example in a trace or log message), the following code will work and has the added benefit of telling the next guy who stumbles across it exactly what you are doing.

int integerValue = 19400320; 
string formatted = string.Format(CultureInfo.InvariantCulture, "{0:N0}", integerValue);

sets formatted to "19,400,320"

C# 7.1 (perhaps earlier?) makes this as easy and nice-looking as it should be, with string interpolation:

var jackpot = 1_000_000; // underscore separators in numeric literals also available since C# 7.0
var niceNumberString = $"Jackpot is {jackpot:n}";
var niceMoneyString = $"Jackpot is {jackpot:C}";

Simpler, using string interpolation instead of String.Format

 $"{12456:n0}"; // 12,456
 $"{12456:n2}"; // 12,456.00

or using yourVariable

 double yourVariable = 12456.0;
 $"{yourVariable:n0}"; 
 $"{yourVariable:n2}"; 

int num = 98765432;
Console.WriteLine(string.Format("{0:#,#}", num));

For example String.Format("{0:0,0}", 1); returns 01, for me is not valid

This works for me

19950000.ToString("#,#", CultureInfo.InvariantCulture));

output 19,950,000

Note that the value that you're formatting should be numeric. It doesn't look like it will take a string representation of a number and format is with commas.

String.Format("0,###.###"); also works with decimal places

You can use a function such as this to format numbers and optionally pass in the desired decimal places. If decimal places are not specified it will use two decimal places.

    public static string formatNumber(decimal valueIn=0, int decimalPlaces=2)
    {
        return string.Format("{0:n" + decimalPlaces.ToString() + "}", valueIn);
    }

I use decimal but you can change the type to any other or use an anonymous object. You could also add error checking for negative decimal place values.

You want same Format value and culture specific.

 Double value= 1234567;
 value.ToString("#,#.##", CultureInfo.CreateSpecificCulture("hi-IN"));

Output: 12,34,567

I tried many of the suggestions above but the below work better for me:

string.Format("{0:##,###.00}", myValue)

but this fails when you have values like 0.2014 where it gives .21 For this I use

string.Format("{0:#,##0.00}", myValue)

Try this:

var number = 123456789;
var str = number.ToString("N0");

Result is: "123,456,789"

If you want to show it in DataGridview , you should change its type , because default is String and since you change it to decimal it considers as Number with floating point

Dim dt As DataTable = New DataTable
dt.Columns.Add("col1", GetType(Decimal))
dt.Rows.Add(1)
dt.Rows.Add(10)
dt.Rows.Add(2)

DataGridView1.DataSource = dt

The method I used to not worry anymore about cultures and potential formatting issues is that I formatted it as currency and took out the currency symbol afterwards.

if (decimal.TryParse(tblCell, out result))

{
  formattedValue = result.ToString("C").Substring(1);
}