Regex for numbers only in C#

Question

I haven't used regular expressions at all, so I'm having difficulty troubleshooting. I want the regex to match only when the contained string is all numbers; but with the two examples below it is matching a string that contains all numbers plus an equals sign like "1234=4321". I'm sure there's a way to change this behavior, but as I said, I've never really done much with regular expressions.

string compare = "1234=4321";
Regex regex = new Regex(@"[\d]");

if (regex.IsMatch(compare))
{ 
    //true
}

regex = new Regex("[0-9]");

if (regex.IsMatch(compare))
{ 
    //true
}

In case it matters, I'm using C# and .NET2.0.

Do you need to match numbers or digits? For example: 123.456 is a number, but it's not all digits. — Joel Coehoorn
– Joel Coehoorn, Commented Nov 7, 2008 at 18:54
Why not TryParse the string for that simple case? bool decimal.TryParse(string string, out decimal result) or bool int.TryParse(string string, out int result) — Makach
– Makach, Commented Nov 3, 2010 at 9:55
Look at this answer for a definitive treatment of parsing numbers with regular expressions. — tchrist
– tchrist, Commented Nov 23, 2010 at 14:53
Try.Parse will accept a plus or minus sign at the start, and leading/trailing spaces. — Robin Bennett
– Robin Bennett, Commented Jan 24, 2011 at 10:40
In general, the easiest way to troubleshoot Regex expressions, in my opinion, is by using a command line interpreter, if your language allows it (seems that most do). Since this example is in C#, you can use linqpad.net, or you could use a breakpoint in the debugger and then use the Immediate window in VS as a CLI. — andrew
– andrew, Commented Feb 18, 2015 at 19:18

Community · Accepted Answer · 2017-05-23 12:26:34Z

625

Use the beginning and end anchors.

Regex regex = new Regex(@"^\d$");

Use "^\d+$" if you need to match more than one digit.

Note that "\d" will match [0-9] and other digit characters like the Eastern Arabic numerals ٠١٢٣٤٥٦٧٨٩. Use "^[0-9]+$" to restrict matches to just the Arabic numerals 0 - 9.

If you need to include any numeric representations other than just digits (like decimal values for starters), then see @tchrist's comprehensive guide to parsing numbers with regular expressions.

edited May 23, 2017 at 12:26

CommunityBot

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answered Nov 7, 2008 at 18:44

Bill the Lizard

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3 Comments

Najeeb Over a year ago

How about a set number of numeric values? This is usually so for postal codes of certain countries like India. I guess we may have to do a string length check after this?

Bill the Lizard Over a year ago

@Najeeb Yes, since Indian zip codes are 6-digit numbers, you can use something like "^\d{6}$". Some other countries have more complicated rules for zip codes, so regex solutions for multiple countries can get pretty complicated too. Check out some of the examples at stackoverflow.com/q/578406/1288

Tobi G. Over a year ago

I use [0-9] instead of \d. It makes RegEx easier to read.

TazGPL · Accepted Answer · 2013-12-16 13:24:13Z

139

Your regex will match anything that contains a number, you want to use anchors to match the whole string and then match one or more numbers:

regex = new Regex("^[0-9]+$");

The ^ will anchor the beginning of the string, the $ will anchor the end of the string, and the + will match one or more of what precedes it (a number in this case).

edited Dec 16, 2013 at 13:24

TazGPL

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answered Nov 7, 2008 at 18:46

Robert Gamble

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Comments

Community · Accepted Answer · 2018-08-22 12:44:36Z

57

If you need to tolerate decimal point and thousand marker

var regex = new Regex(@"^-?[0-9][0-9,\.]+$");

You will need a "-", if the number can go negative.

edited Aug 22, 2018 at 12:44

CommunityBot

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answered Apr 19, 2011 at 13:21

Andrew Chaa

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5 Comments

Andrew Chaa Over a year ago

@Florin Ghita. Thanks. "-" needs to be at the beginning.

DavidRR Over a year ago

This regex also wrongly permits the leading negative sign (-) and period (.) to occur more than once.

butterywombat Over a year ago

you can make - and . optional via ?. -?\d+(?:\.\d+)? would match integers or decimals. (The ?: in the parens just makes the parens a non-capturing group and used to only group for clarity.)

PrivateOmega Over a year ago

It fails for edge cases like 1,.5 , but if you oversee that. still it fails for basic cases like -2. Please alter it to ^-?[0-9][0-9,\.]*$ to avoid failing for the basic case. + is replaced with *

Sadiq Khoja Over a year ago

doesn't matches "0"

Sigmarod · Accepted Answer · 2023-06-21 13:44:23Z

25

This works with integers and decimal numbers. It doesn't match if the number has the coma thousand separator ,

"^-?\\d*(\\.\\d+)?$"

Some strings that match with this:

Some strings that don't:

hello
9bye
hello9bye
888,323
5,434.3
-8,336.09
87078.

edited Jun 21, 2023 at 13:44

Sigmarod

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answered Mar 1, 2014 at 8:47

ultraklon

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2 Comments

Amine KOUIS Over a year ago

How can i mach big number like 2.3e-5. I checked this demo and it doesn't work.

mernst Over a year ago

This matches the empty string.

kasperjj · Accepted Answer · 2008-11-07 18:45:33Z

21

It is matching because it is finding "a match" not a match of the full string. You can fix this by changing your regexp to specifically look for the beginning and end of the string.

^\d+$

answered Nov 7, 2008 at 18:45

kasperjj

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1 Comment

Amine KOUIS Over a year ago

It doesn't work for negative or decimal number. Check this demo.

Rezo Megrelidze · Accepted Answer · 2014-01-21 20:15:59Z

20

Perhaps my method will help you.

    public static bool IsNumber(string s)
    {
        return s.All(char.IsDigit);
    }

edited Jan 21, 2014 at 20:15

answered Jan 21, 2014 at 19:31

Rezo Megrelidze

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2 Comments

DavidRR Over a year ago

Keep in mind though that Char.IsDigit returns true for any character that is a member of the UnicodeCategory.DecimalDigitNumber category. This may not be what the OP wants. Also see Why Char.IsDigit returns true for chars which can't be parsed to int?.

DavidRR Over a year ago

See Unicode Characters in the 'Number, Decimal Digit' Category.

Maicon Mauricio · Accepted Answer · 2021-06-12 20:24:16Z

19

If you need to check if all the digits are number (0-9) or not,

^[0-9]+$

Matches

And does not match

154a25
1234=3254

edited Jun 12, 2021 at 20:24

Maicon Mauricio

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answered May 22, 2014 at 5:20

Ujjal Suttra Dhar

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Comments

fnc12 · Accepted Answer · 2014-04-04 09:16:01Z

14

Sorry for ugly formatting. For any number of digits:

[0-9]*

For one or more digit:

[0-9]+

answered Apr 4, 2014 at 9:16

fnc12

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Comments

Mark Brackett · Accepted Answer · 2008-11-07 18:47:30Z

11

^\d+$, which is "start of string", "1 or more digits", "end of string" in English.

answered Nov 7, 2008 at 18:47

Mark Brackett

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Comments

Marina · Accepted Answer · 2015-12-05 15:32:37Z

11

Here is my working one:

^(-?[1-9]+\\d*([.]\\d+)?)$|^(-?0[.]\\d*[1-9]+)$|^0$

And some tests

Positive tests:

string []goodNumbers={"3","-3","0","0.0","1.0","0.1","0.0001","-555","94549870965"};

Negative tests:

string []badNums={"a",""," ","-","001","-00.2","000.5",".3","3."," -1","--1","-.1","-0"};

Checked not only for C#, but also with Java, Javascript and PHP

edited Dec 5, 2015 at 15:32

answered Nov 28, 2015 at 20:23

Marina

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2 Comments

Tagar Over a year ago

".3","3." are actually good numbers (meaning 0.3 and 3.0 respectively). we see this all the time in source systems, and most to_number(xx) functions of the languages you have mentioned will recognize and conver them correctly. thanks.

Marina Over a year ago

@Ruslan you are right that in many systems ".3","3." would parse to valid number and used as you mentioned "0.3" and "3.0". But in the other hand - that is converted value, so original value ".3" and "3." isn't really existing number.

Oli Folkerd · Accepted Answer · 2020-08-25 17:54:13Z

9

Use beginning and end anchors.

 Regex regex = new Regex(@"^\d$");

Use "^\d+$" if you need to match more than one digit.

edited Aug 25, 2020 at 17:54

Oli Folkerd

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answered Jul 6, 2016 at 10:42

lipika chakraborty

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Comments

S.M.Mousavi · Accepted Answer · 2012-04-28 21:38:10Z

7

Another way: If you like to match international numbers such as Persian or Arabic, so you can use following expression:

Regex = new Regex(@"^[\p{N}]+$");

To match literal period character use:

Regex = new Regex(@"^[\p{N}\.]+$");

answered Apr 28, 2012 at 21:38

S.M.Mousavi

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Comments

tripleee · Accepted Answer · 2021-06-12 18:44:01Z

7

While non of the above solutions was fitting my purpose, this worked for me.

var pattern = @"^(-?[1-9]+\d*([.]\d+)?)$|^(-?0[.]\d*[1-9]+)$|^0$|^0.0$";
return Regex.Match(value, pattern, RegexOptions.IgnoreCase).Success;

Example of valid values:

"3",
"-3",
"0",
"0.0",
"1.0",
"0.7",
"690.7",
"0.0001",
"-555",
"945465464654"

Example of not valid values:

"a",
"",
" ",
".",
"-",
"001",
"00.2",
"000.5",
".3",
"3.",
" -1",
"--1",
"-.1",
"-0",
"00099",
"099"

edited Jun 12, 2021 at 18:44

tripleee

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answered Sep 12, 2016 at 8:51

Daniele D.

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4 Comments

Eduardo Herrera Over a year ago

you can give me more details, because it unfolds a mistake

Eduardo Herrera Over a year ago

i put on textbox_changed

Eduardo Herrera Over a year ago

private void textBox2_TextChanged(object sender, EventArgs e) { var pattern = @"^(-?[1-9]+\d*([.]\d+)?)$|^(-?0[.]\d*[1-9]+)$|^0$|^0.0$"; return Regex.Match(textBox1.Text, pattern, RegexOptions.IgnoreCase).Success; }

Daniele D. Over a year ago

@EduardoHerrera what is the mistake?

Tagar · Accepted Answer · 2020-06-03 01:08:56Z

6

Regex for integer and floating point numbers:

^[+-]?\d*\.\d+$|^[+-]?\d+(\.\d*)?$

A number can start with a period (without leading digits(s)), and a number can end with a period (without trailing digits(s)). Above regex will recognize both as correct numbers.

A . (period) itself without any digits is not a correct number. That's why we need two regex parts there (separated with a "|").

Hope this helps.

edited Jun 3, 2020 at 1:08

answered Feb 22, 2016 at 4:11

Tagar

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1 Comment

Renato Medeiros Over a year ago

This is the most complete solution. Congrats!

Azur · Accepted Answer · 2016-09-01 08:10:59Z

3

I think that this one is the simplest one and it accepts European and USA way of writing numbers e.g. USA 10,555.12 European 10.555,12 Also this one does not allow several commas or dots one after each other e.g. 10..22 or 10,.22 In addition to this numbers like .55 or ,55 would pass. This may be handy.

^([,|.]?[0-9])+$

answered Sep 1, 2016 at 8:10

Azur

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1 Comment

Christoph Over a year ago

There is no single European way of writing numbers. We (de-CH) would write 10'555.12 (and our "Bundeskanzlei" 10 555,12).

Chathuranga Kasthuriarachchi · Accepted Answer · 2020-11-12 05:01:30Z

3

 console.log(/^(0|[1-9][0-9]*)$/.test(3000)) // true

answered Nov 12, 2020 at 5:01

Chathuranga Kasthuriarachchi

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1 Comment

Elletlar Over a year ago

While this code may answer the question, providing additional context regarding why and/or how this code answers the question improves its long-term value. How to Answer

James Selvakumar · Accepted Answer · 2010-11-03 09:50:59Z

2

If you want to extract only numbers from a string the pattern "\d+" should help.

answered Nov 3, 2010 at 9:50

James Selvakumar

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Comments

Yawar Ali · Accepted Answer · 2021-09-02 13:47:28Z

0

To check string is uint, ulong or contains only digits one .(dot) and digits Sample inputs

Regex rx = new Regex(@"^([1-9]\d*(\.)\d*|0?(\.)\d*[1-9]\d*|[1-9]\d*)$");
string text = "12.0";
var result = rx.IsMatch(text);
Console.WriteLine(result);

Samples

123 => True
123.1 => True
0.123 => True
.123 => True
0.2 => True
3452.434.43=> False
2342f43.34 => False
svasad.324 => False
3215.afa => False

answered Sep 2, 2021 at 13:47

Yawar Ali

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Programmer · Accepted Answer · 2021-09-28 07:07:44Z

0

The following regex accepts only numbers (also floating point) in both English and Arabic (Persian) languages (just like Windows calculator):

^((([0\u0660\u06F0]|([1-9\u0661-\u0669\u06F1-\u06F9][0\u0660\u06F0]*?)+)(\.)[0-9\u0660-\u0669\u06F0-\u06F9]+)|(([0\u0660\u06F0]?|([1-9\u0661-\u0669\u06F1-\u06F9][0\u0660\u06F0]*?)+))|\b)$

The above regex accepts the following patterns:

11
1.2
0.3
۱۲
۱.۳
۰.۲
۲.۷

The above regex doesn't accept the following patterns:

3.
.3
0..3
.۱۲

edited Sep 28, 2021 at 7:07

answered Jun 12, 2021 at 4:57

Programmer

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Mahozad · Accepted Answer · 2025-09-09 08:38:15Z

0

This matches Latin/ASCII and non-Latin decimal digits too (a little similar to S.M.Mousavi answer):

var regex = new Regex(@"^\p{Nd}$"); // Matches more than 700 types of digits

^ is for start of string, $ for end of string
\p{something} matches a Unicode character category/class/collection
Nd means numbers (digits) that are based 10 (decimal)
Uppercase \P{something} means negated (everything except)

edited Sep 9 at 8:38

answered Sep 9 at 8:33

Mahozad

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Giri babu vuppula · Accepted Answer · 2015-05-01 22:56:14Z

-4

Regex regex = new Regex ("^[0-9]{1,4}=[0-9]{1,4]$")

answered May 1, 2015 at 22:56

Giri babu vuppula

13

1 Comment

Wai Ha Lee Over a year ago

Can you explain your answer a bit please? You'll notice that the other answers to this question have some level of explanation of what each part of the regex does, which you are lacking.

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