In C#, how to check whether a string contains an integer?

Question

I just want to know, whether a String variable contains a parsable positive integer value. I do NOT want to parse the value right now.

Currently I am doing:

int parsedId;
if (
    (String.IsNullOrEmpty(myStringVariable) ||
    (!uint.TryParse(myStringVariable, out parsedId))
)
{//..show error message}

This is ugly - How to be more concise?

Note: I know about extension methods, but I wonder if there is something built-in.

@MatthewWatson Thanks for spotting this. It's positive only in my case, clarified the question. — Marcel, Aug 15 '13 at 11:52
Change from `int.TryParse` to `uint.TryParse` to have strings that look like negative integers return false. — Jeppe Stig Nielsen, Aug 15 '13 at 11:55

DGibbs · Answer 1 · 2017-06-09T14:29:40.937

148

You could use char.IsDigit:

     bool isIntString = "your string".All(char.IsDigit)

Will return true if the string is a number

    bool containsInt = "your string".Any(char.IsDigit)

Will return true if the string contains a digit

edited Jun 09 '17 at 14:29

answered Aug 15 '13 at 11:40

DGibbs

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If `str` is equal to `"iuhs,./hu3dwuh"`, then `str.Any(char.IsDigit)` will be true. – Jeppe Stig Nielsen Aug 15 '13 at 11:47
3

I'm not the downvoter, but 1. There's no static function on the `string` class called `Any` (presumably you meant for the string variable to be called `string`, but that's not possible); 2. If you're referring to the Linq extension method `Any`, you have to call it liks this: `s.Any(c => char.IsDigit(c))`; 3. I think he wants the *whole* string to be an integer, not just to contain a digit somewhere; otherwise it makes no sense for him to use `int.TryParse`. – Magnus Grindal Bakken Aug 15 '13 at 11:48
6

@MagnusGrindalBakken Regarding your (2): No, since the signature and return type is correct, the expression `char.IsDigit` (a so-called method group) _can_ be converted to type `Func` through an implicit conversion, so that part is OK. – Jeppe Stig Nielsen Aug 15 '13 at 11:50
1

@JeppeStigNielsen Good call. I always forget about that. – Magnus Grindal Bakken Aug 15 '13 at 11:52
I upvoted but it would be nice if you could update your answer to be correct linq like Magnus suggested. – TroySteven Jan 28 '20 at 14:54
1

@TroySteven - He's wrong though? You don't have to use lambda syntax e.g `s.Any(x => char.IsDigit(x))` you can just pass `char.IsDigit` as a delegate, try it... https://dotnetfiddle.net/qS59c0 and the first example satisfies the 'whole string is an integer' – DGibbs Jan 28 '20 at 15:55

score 37 · Answer 2 · answered Aug 15 '13 at 11:38

37

Assuming you want to check that all characters in the string are digits, you could use the Enumerable.All Extension Method with the Char.IsDigit Method as follows:

bool allCharactersInStringAreDigits = myStringVariable.All(char.IsDigit);

answered Aug 15 '13 at 11:38

dtb

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What if `myStringVariable` contains digit characters from many different "scripts" from all over the world, such as Hindu-Arabic numerals combined with western numerals? – Jeppe Stig Nielsen Aug 15 '13 at 11:45
In that case, "۲۲۲" will give true, but parsing it as an int will throw an exception. – Matthew Watson Aug 15 '13 at 12:34
1

If you wanted to check if any of the characters was numeric and not all of them, you could use - bool anyCharactersInStringAreDigits = myStringVariable.Any(char.IsDigit); – Deano Jan 10 '14 at 16:03

score 33 · Answer 3 · answered Dec 14 '15 at 22:11

33

Maybe this can help

string input = "hello123world";
bool isDigitPresent = input.Any(c => char.IsDigit(c));

answer from msdn.

answered Dec 14 '15 at 22:11

panako

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This is wrong. It will check whether some digits are present, but not whether the string as a whole does represent an integer value. – Marcel Apr 12 '19 at 07:49
10

The requirements of the question are whether a string *Contains* parsable integer, not whether or not the entire string represents an number. – Gichamba Mar 20 '20 at 11:45

Sergey Berezovskiy · Answer 4 · 2013-08-15T11:49:08.090

8

You can check if string contains numbers only:

Regex.IsMatch(myStringVariable, @"^-?\d+$")

But number can be bigger than Int32.MaxValue or less than Int32.MinValue - you should keep that in mind.

Another option - create extension method and move ugly code there:

public static bool IsInteger(this string s)
{
   if (String.IsNullOrEmpty(s))
       return false;

   int i;
   return Int32.TryParse(s, out i);
}

That will make your code more clean:

if (myStringVariable.IsInteger())
    // ...

edited Aug 15 '13 at 11:49

answered Aug 15 '13 at 11:38

Sergey Berezovskiy

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straight forward answer – Radhe Sham Nov 28 '17 at 11:49
Nice. I have enhanced your method to handle array of string. `public static bool IsInteger(this string[] str) { bool isInteger = false; if (str == null) return isInteger; foreach (var s in str) { if (String.IsNullOrEmpty(s)) return isInteger; int i; isInteger = Int32.TryParse(s, out i); if (isInteger == false) return isInteger; } return isInteger; }` – Ashish Kumar Jaryal Jan 16 '19 at 15:08

score 5 · Answer 5 · answered Apr 12 '19 at 07:04

5

This work for me.

("your string goes here").All(char.IsDigit)

answered Apr 12 '19 at 07:04

sarmad salik

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1

Thanks for your contribution. But however, this is a repetition of the answer @dtb already gave some years ago. – Marcel Apr 12 '19 at 07:47

SBoss · Answer 6 · 2013-08-15T12:09:13.907

4

Sorry, didn't quite get your question. So something like this?

str.ToCharArray().Any(char.IsDigit);

Or does the value have to be an integer completely, without any additional strings?

if(str.ToCharArray().All(char.IsDigit(c));

edited Aug 15 '13 at 12:09

answered Aug 15 '13 at 11:38

SBoss

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What would your second answer return for `-----` ? – I4V Aug 15 '13 at 11:54
@SBoss It should exactly be parsable as int, but I just want to now that, not the result of the parsing value. – Marcel Aug 15 '13 at 11:56
Just realised that ;) – SBoss Aug 15 '13 at 11:56
Sorry Marcel, I should have read your question better. My second answer isn't really much prettier, but it's an alternative. – SBoss Aug 15 '13 at 11:57
I get the first downvote for missing the point of the question, but since I modified my answer, why the second one? – SBoss Aug 15 '13 at 12:21

score 3 · Answer 7 · edited Oct 16 '20 at 13:00

        string text = Console.ReadLine();
        bool isNumber = false;

        for (int i = 0; i < text.Length; i++)
        {
            if (char.IsDigit(text[i]))
            {
                isNumber = true;
                break;
            }
        }

        if (isNumber)
        {
            Console.WriteLine("Text contains number.");
        }
        else
        {
            Console.WriteLine("Text doesn't contain number.");
        }

        Console.ReadKey();

Or Linq:

        string text = Console.ReadLine();

        bool isNumberOccurance =text.Any(letter => char.IsDigit(letter));
        Console.WriteLine("{0}",isDigitPresent ? "Text contains number." : "Text doesn't contain number.");
        Console.ReadKey();

score 2 · Accepted Answer · answered Aug 15 '13 at 11:54

2

The answer seems to be just no.

Although there are many good other answers, they either just hide the uglyness (which I did not ask for) or introduce new problems (edge cases).

answered Aug 15 '13 at 11:54

Marcel

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I guess the designers of C# could introduce some new syntactic sugar for this case where we don't care about the out variable. It could look like `int.TryParse(myStringVariable, out void)` or something. The compiler should then automatically introduce a "generated" local variable of the correct type, but it would not look ugly in code. Of course the generated variable would not be accessible (should have some "crazy" illegal name). – Jeppe Stig Nielsen Aug 15 '13 at 12:01

In C#, how to check whether a string contains an integer?

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