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C# - Need help with my regular expression

Posted on 2009-05-20
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Last Modified: 2012-05-07
Hi all,

can someone help me with my regular expression. I have already read many pages about regular expressions, but I just don't seem to get it in general.

The function below need to check if the control_string is positive, contains only numbers and needs tot start with 1-9 followed by zero or more other numbers.

So "1", "12", "230" are ok, but "01", "a", "23c" etc. are wrong (all without the quotes of course). At the moment it works for the most part, but it also accepts "01".

What am I doing wrong?

I hope you guys can help me out.
public static Boolean checkIt(string control_string)
{
    Regex objNotNaturalPattern = new Regex("[^0-9]");
    Regex objNaturalPattern = new Regex("[1-9][0-9]*");
 
    return (!objNotNaturalPattern.IsMatch(control_string) && objNaturalPattern.IsMatch(control_string));
 
}

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Question by:fourice
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Accepted Solution

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ozo earned 125 total points
ID: 24429794
^[1-9][0-9]*$
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Author Comment

by:fourice
ID: 24429821
Thanks, it works!
Is it possible that you explain a bit how I can 'read' this pattern?
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Author Closing Comment

by:fourice
ID: 31583417
Works like a charm, but in my effort to understand regular expressions, I would like to know how to 'read' the pattern.
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Author Comment

by:fourice
ID: 24429842
I forgot to ask, what was wrong with my original pattern?
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Expert Comment

by:ozo
ID: 24429855
 ^                        the beginning of the string
----------------------------------------------------------------------
  [1-9]                    any character of: '1' to '9'
----------------------------------------------------------------------
  [0-9]*                   any character of: '0' to '9' (0 or more
                           times (matching the most amount possible))
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string

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