.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

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

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

That will give you commas at the relevant points.

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}";

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.

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