c# check for integers in a textbox

Question

I am trying to check if a textbox contains a number. The problem is that it always returns that it contains a non-numeric character. I've tried several ways, but none of them seems to work.

One of the ways I've tried is:

if( Regex.IsMatch(tb.Text.Trim(), @"^[0-9]+$")) // tb.Text is the textbox

It does not matter what I enter in the textbox, it always returns that it contains a non-numeric character (I tried entering 1-9, 'a', 'b')

Yes, I tried it with just 1 character and with multiple characters — wesley221, Apr 14 '14 at 11:03
Why do you use such a complicated regex instead of "\d"? See http://stackoverflow.com/questions/3180354/regex-check-if-string-contains-at-leat-one-digit — Blackunknown, Apr 14 '14 at 11:06
Do you want to parse the `TextBox` value or do you want to check if it contains numbers? — Guilherme Oliveira, Apr 14 '14 at 11:15
I want to check if the textbox contains any number, if it does not contain any number I want it to give an error. Therefore i tried this: `if( Regex.IsMatch(tb.Text.Trim(), @"\d")) { Debug.WriteLine(tb.Text); containsLetter = true; break; }` If i enter 3 in the textbox, it returns the value 3 in the debug window. — wesley221, Apr 14 '14 at 11:27
@wesley221 I don't know what validation you're doing before calling this Regex, cause for me it worked. Did you check if your `TextBox` contains any value? — Guilherme Oliveira, Apr 14 '14 at 11:29
@GuilhermeOliveira I know for sure that the textbox isnt empty, since the debug window shows me the value from the textbox (also I just added a tb.Text != isnull to the statement, this didn't affect the result). Before the RegEx I don't have any validation, so as far as I know that cant be the problem. — wesley221, Apr 14 '14 at 11:33
@wesley221 This `Regex` should work. Did you try `abc123` to see if it matches? — Guilherme Oliveira, Apr 14 '14 at 11:45
your regex fails because the way you put it you declare that it shall only be numbers as indicated by ^(start) and $(end). if you leave out that bit it should work — Dbl, Apr 14 '14 at 12:13

SWeko · Answer 1 · 2014-04-14T11:14:13.080

You could just parse the string to a specific number type, i.e.

double result;
if (!double.TryParse(tb.Text, out result))
{
  //text is not a valid double;
  throw new Exception("not a valid number");
}
//else the value is within the result variable

From your regex it seems that you need only integer values, so you should use int.TryParse or long.TryParse instead.

Quick and dirty test program:

void Main()
{
    TestParse("1");
    TestParse("a");
    TestParse("1234");
    TestParse("1a");
}

void TestParse(string text)
{
  int result;
  if (int.TryParse(text, out result))
  {
    Console.WriteLine(text + " is a number");
  }
  else
  {
    Console.WriteLine(text + " is not a number");
  }
}

Results:

1 is a number 
a is not a number  
1234 is a number  
1a is not a number

score 2 · Answer 2 · answered Apr 14 '14 at 11:04

2

You could replace your Regex for this:

if(Regex.IsMatch(tb.Text.Trim(), @"[0-9]"))

Or for this:

if(Regex.IsMatch(tb.Text.Trim(), @"\d"))

answered Apr 14 '14 at 11:04

Guilherme Oliveira

2,008
3
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1

Nice edit, was just about to ask you to read the comment above. – Blackunknown Apr 14 '14 at 11:08
what is mean by \d can you explain me the expression, i am very new to regex – Ehsan Sajjad Apr 14 '14 at 11:09
@Blackunknown Yes, you remembered me that `\d` exists too. – Guilherme Oliveira Apr 14 '14 at 11:10
@EhsanSajjad `\d` is to match with decimal characters – Guilherme Oliveira Apr 14 '14 at 11:10
I knew about both of those, and they dont seem to work either – wesley221 Apr 14 '14 at 11:11
@wesley221 Actually they work here for me. My string contains `abc123` and it matches. – Guilherme Oliveira Apr 14 '14 at 11:13
@wesley221 try this site: http://regexhero.net/tester/ put the regex and your text and check whether it contains numbers or not. – Guilherme Oliveira Apr 14 '14 at 11:16

score 1 · Answer 3 · edited Apr 14 '14 at 11:06

1

you can use TryParse:

int value;

bool IsNumber = int.TryParse(tb.Text.Trim(), out value);

if(IsNumber)
{
    //its number
}

edited Apr 14 '14 at 11:06

helb

7,609
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answered Apr 14 '14 at 11:04

Ehsan Sajjad

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I just tried this way, it does not work. It still returns that it contains a non-numeric character – wesley221 Apr 14 '14 at 11:07
it should work if its not a number, what you enterd? – Ehsan Sajjad Apr 14 '14 at 11:08
I entered '3' in the textbox, aswell 'a', both of them returned true – wesley221 Apr 14 '14 at 11:10
you enterd 3 and a simultaneously – Ehsan Sajjad Apr 14 '14 at 11:11
First attempt it was a '3', next attempt was the 'a'. – wesley221 Apr 14 '14 at 11:12
1

you must be doing something, i tested on my system it worked. – Ehsan Sajjad Apr 14 '14 at 11:19
Double-check the basics: That you're reading from the correct textbox, something else doesn't change its value etc. Put a breakpoint before that part and see the value of tb.Text. – George T Apr 14 '14 at 12:10

score 1 · Answer 4 · answered Apr 14 '14 at 11:35

private void btnMove_Click(object sender, EventArgs e)
        {
            string check = txtCheck.Text;
            string status = "";
            for (int i = 0; i < check.Length; i++)
            {
                if (IsNumber(check[i]))
                status+="The char at "+i+" is a number\n";
            }
            MessageBox.Show(status);
        }
        private bool IsNumber(char c)
        {
            return Char.IsNumber(c);
        }

c# check for integers in a textbox

4 Answers4