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Question

How do I determine if there are two or one numbers at the start of my string?

Answer 1

+5 A:

Use a regular expression:

using System.Text.RegularExpressions;

str = "35|http:\/\/v10.lscache3.c.youtube.com\/videoplayback...";

Regex r = new Regex(@"^[0-9]{1,2}");
Match m = r.Match(str);    
if(m.Success) {
    Console.WriteLine("Matched: " + m.Value);
} else {
    Console.WriteLine("No match");
}

will capture 1-2 digits at the beginning of the string.

burkestar 2010-09-28 01:25:30

can use `\d` in place of `[0-9]` and the outter `()` s aren't necessary methinks

Mark 2010-09-28 01:34:14

or [:digit:] should work too...parenthesis are needed for capture group

burkestar 2010-09-28 01:35:20

...and you can use m.Success() if you expect there may be lines without numbers

Les 2010-09-28 01:38:02

@burkestar in this case there's no need for the capture group. Mark is right that they can be omitted. Keeping them doesn't hurt, but by using `m.Value` you're actually not referencing the capture group. To do so you would use `m.Groups[1].Value`. Since this regex starts at the beginning of the string and isn't matching anything but digits you can omit the `()` and use `m.Value`.

Ahmad Mageed 2010-09-28 01:38:11

@Les Good point, but it's a property, so just `m.Success`: `if (m.Success) { // do something } else { // no match }`

Ahmad Mageed 2010-09-28 01:39:55

-1. abuse of regex when it's not really the best way to do it

Lie Ryan 2010-09-28 02:02:00

regex is efficient, flexible if more advanced cases need to be considered, easy to understand and works since .NET 1.1. Linq requires .NET Framework 3.5.

burkestar 2010-09-28 02:06:24

using regex just to capture 1 or 2 digits in a well-known position (index 0) is like using a sledge hammer to kill an ant

Lie Ryan 2010-09-28 02:20:39

@Lie Ryan - 1) it is the OPs choice, 2) simple requirements seldom remain simple, 3) others reading this may have similar problem but need a more flexible solution than int.Parse().

Les 2010-09-28 15:41:31

Answer 2

+5 A:

You can use LINQ:

string s = "35|...";

int result = int.Parse(new string(s.TakeWhile(char.IsDigit).ToArray()));

or (if the number is always followed by a |) good ol' string manipulation:

string s = "35|...";

int result = int.Parse(s.Substring(0, s.IndexOf('|')));

dtb 2010-09-28 01:26:23

+1 looks like you were first with the LINQ approach :)

Ahmad Mageed 2010-09-28 01:31:02

Thank-you this is a simple self-explanatory answer. It is very useful to young programmers like me.

Liam E-p 2010-09-28 01:31:55

can also use split and limit the number of splits, if he wants to do something with the other chunk

Mark 2010-09-28 01:35:40

How would you remove the number after you have parsed it?

Liam E-p 2010-09-28 02:04:27

Like the use of TakeWhile, I haven't used this extention as yet.

Harry 2010-09-28 02:40:10

@Liam: Exactly. Try `s.Split(new char[] {'|'}, 2)` instead. it returns an array, the first one containing your number as a string, which you can `int.Parse`, and the second one containing the rest of the string w/ the number removed

Mark 2010-09-28 02:42:35

Answer 3

A:

if you know that the number is always going to be 2 digits:

string str = "35|http:\/\/v10.lscache3.c.youtube.com\/videoplayback?...";
int result;
if (!int.TryParse(str.Substring(0, 2), out result)) {
    int.TryParse(str.Substring(0, 1), out result)
}
// use the number

if you're not sure how long the number is, look at the .indexOf() approach by dtb. If you need something much more complex, only then consider using regex.

Lie Ryan 2010-09-28 02:09:11

Answer 4

A:

You can get the two first characters and convert to int.

var s = "a35|...";
short result = 0;
bool isNum = Int16.TryParse(s.Substring(0, 2), out result);

BrunoLM 2010-09-28 02:36:55

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How do I determine if there are two or one numbers at the start of my string?

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