How can I format a number into a string with leading zeros?

Question

I have a number that I need to convert to a string. First I used this:

Key = i.ToString();

But I realize it's being sorted in a strange order and so I need to pad it with zeros. How could I do this?

possible duplicate of [C# convert int to string with padding zeros?](http://stackoverflow.com/questions/4325267/c-sharp-convert-int-to-string-with-padding-zeros) — nawfal, Jun 04 '15 at 07:46

score 444 · Accepted Answer · edited Mar 27 '15 at 09:52

444

Rather simple:

Key = i.ToString("D2");

D stands for "decimal number", 2 for the number of digits to print.

edited Mar 27 '15 at 09:52

Peter Mortensen

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answered Mar 24 '11 at 11:31

Mario

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if you use `string.Format("D2", value)` you'll get `D2` in the output. this doesn't work. We must use `"{0:00}"` in this case. – v.oddou Aug 07 '15 at 07:22
58

You should use `string.Format("{0:D2}", value)` instead. Just saying `string.Format("D2", ...)` won't replace anything no matter what since you don't have a placeholder. – infinitypanda Sep 11 '15 at 19:25
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@infinitypanda realize that this will only work when `value` is an int. If `value` is a double, for instance, it will have to be `string.Format("{0:00}", value)` – derekantrican Feb 23 '17 at 15:02
if we are talking about 'leading digits' I think the answer would be i.ToString("00"); where "00" represents the leading zeros.. you can increase this amount as much as possible. – Dedan Feb 01 '19 at 13:38
This will fail with `System.FormatException` if the number is a **decimal**. Better to use `.ToString("N0").PadLeft(2, '0')`. However, `PadLeft` does not work properly with negative numbers (zeros in front of negative sumbol). – Codingwiz Feb 14 '23 at 17:10

Paul · Answer 2 · 2019-01-23T14:21:40.540

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See String formatting in C# for some example uses of String.Format

Actually a better example of formatting int

String.Format("{0:00000}", 15);          // "00015"

or use String Interpolation:

$"{15:00000}";                           // "00015"

edited Jan 23 '19 at 14:21

answered Mar 24 '11 at 11:26

Paul

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Note that String.Format("{0:00000}", "15"); returns "15", i.e. it does not work on a string. – Paul McCarthy May 10 '19 at 11:42
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Even shorter way: `$"{15:D5}";` will result in an output of: `"00015"`. – Al Dass Sep 23 '20 at 20:50
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If you have `int i` and want 8 digits, simply use `var iStr = $"{i:D8}`. – Matt Feb 09 '22 at 10:35

score 90 · Answer 3 · edited Feb 28 '18 at 11:01

90

If you like to keep it fixed width, for example 10 digits, do it like this

Key = i.ToString("0000000000");

Replace with as many digits as you like.

i = 123 will then result in Key = "0000000123".

edited Feb 28 '18 at 11:01

gog

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answered Mar 24 '11 at 11:26

Øyvind Bråthen

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score 78 · Answer 4 · answered Apr 10 '16 at 22:25

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Since nobody has yet mentioned this, if you are using C# version 6 or above (i.e. Visual Studio 2015) then you can use string interpolation to simplify your code. So instead of using string.Format(...), you can just do this:

Key = $"{i:D2}";

answered Apr 10 '16 at 22:25

DavidG

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firefox1986 · Answer 5 · 2015-05-08T13:46:51.873

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use:

i.ToString("D10")

See Int32.ToString (MSDN), and Standard Numeric Format Strings (MSDN).

Or use String.PadLeft. For example,

int i = 321;
Key = i.ToString().PadLeft(10, '0');

Would result in 0000000321. Though String.PadLeft would not work for negative numbers.

See String.PadLeft (MSDN).

edited May 08 '15 at 13:46

answered Mar 24 '11 at 11:27

firefox1986

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I'd guess that will screw you once you try to use it with negative numbers. – Mario Mar 24 '11 at 11:32
Thanks - I used the second one. I left out the ".ToString()" - it still works. – SunsetQuest Mar 25 '19 at 04:07

score 26 · Answer 6 · answered Jun 18 '19 at 14:26

26

For interpolated strings:

$"Int value: {someInt:D4} or {someInt:0000}. Float: {someFloat: 00.00}"

answered Jun 18 '19 at 14:26

Alan Samet

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This is basically the same as the [answer](https://stackoverflow.com/a/36536254/1663001) I posted 3 years before you. – DavidG Jun 29 '23 at 12:52

score 15 · Answer 7 · answered Apr 16 '13 at 06:14

15

Usually String.Format("format", object) is preferable to object.ToString("format"). Therefore,

String.Format("{0:00000}", 15);

is preferable to,

Key = i.ToString("000000");

answered Apr 16 '13 at 06:14

Chameera Dedduwage

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Yes, as @cja asked, why is it preferable? And I'm not arguing against the assertion, I'd like to know why. – Christopher King Aug 14 '15 at 14:16
First syntax "feels" more precise, predictable, and clear. And it would be better stated as Key = String.Format("{0:00000}", 15); that is being compared to Key = i.ToString("000000"); With the first syntax, I'm pretty sure I know exactly the result I'll get, and if bychance I'm one character off, I know exactly what to change (format string. So, in short, to me it's preferable for emotional personal preference, weakly supported by one almost-plausible half-reason ;-) So it's decided then? – Developer63 Feb 07 '20 at 04:01

score 15 · Answer 8 · answered Mar 24 '11 at 11:25

15

Try:

Key = i.ToString("000000");

Personally, though, I'd see if you can't sort on the integer directly, rather than the string representation.

answered Mar 24 '11 at 11:25

Marc Gravell

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score 4 · Answer 9 · edited Feb 21 '19 at 13:48

4

int num=1;
string number=num.ToString().PadLeft(4, '0')

Output="00001"

EDIT: Changed to match the PadLeft amount

edited Feb 21 '19 at 13:48

maeneak

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answered Apr 04 '17 at 10:45

Gayan Chinthaka Dharmarathna

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score 3 · Answer 10 · answered Jun 21 '17 at 06:31

Here I want my no to limit in 4 digit like if it is 1 it should show as 0001,if it 11 it should show as 0011..Below are the code.

        reciptno=1;//Pass only integer.

        string formatted = string.Format("{0:0000}", reciptno);

        TxtRecNo.Text = formatted;//Output=0001..

I implemented this code to generate Money receipt no.

score 2 · Answer 11 · answered Apr 01 '21 at 07:50

2

I found a better way tried all the way but not worked for me

Convert.ToDecimal(LN).ToString("000000#");

LN is Int64

answered Apr 01 '21 at 07:50

Monzur

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How can I format a number into a string with leading zeros?

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