C# Regex.Match to decimal

Question

I have a string "-4.00 %" which I need to convert to a decimal so that I can declare it as a variable and use it later. The string itself is found in string[] rows. My code is as follows:

foreach (string[] row in rows)
{
string row1 = row[0].ToString();
Match rownum = Regex.Match(row1.ToString(), @"\-?\d+\.+?\d+[^%]");
string act = Convert.ToString(rownum); //wouldn't convert match to decimal
decimal actual = Convert.ToDecimal(act);
textBox1.Text = (actual.ToString());
}

This results in "Input string was not in a correct format." Any ideas?

Thanks.

possible duplicate of [How to convert percentage string to double?](http://stackoverflow.com/questions/2171615/how-to-convert-percentage-string-to-double) — RB., Jun 12 '12 at 10:36
Presumably `act` contains a string with a percent sign at the end? For obvious reasons this can't be parsed to a decimal. Modify your regex to use a capturing group (so that it captures the value but not the percentage) and Convert that captured value instead — WickyNilliams, Jun 12 '12 at 10:37

score 3 · Answer 1 · answered Jun 12 '12 at 10:40

I see two things happening here that could contribute.

You are treating the Regex Match as though you expect it to be a string, but what a Match retrieves is a MatchGroup.

Rather than converting rownum to a string, you need to lookat rownum.Groups[0].

Secondly, you have no parenthesised match to capture. @"(\-?\d+\.+?\d+)%" will create a capture group from the whole lot. This may not matter, I don't know how C# behaves in this circumstance exactly, but if you start stretching your regexes you will want to use bracketed capture groups so you might as well start as you want to go on.

You actually need rownum.Groups[0].Value (this is the string), but +1 nevertheless because of the good explanation — executor, Jun 12 '12 at 11:04

WickyNilliams · Accepted Answer · 2012-06-13T10:47:20.180

2

Here's a modified version of your code that changes the regex to use a capturing group and explicitly look for a %. As a consequence, this also simplifies the parsing to decimal (no longer need an intermediary string):

EDIT : check rownum.Success as per executor's suggestion in comments

string[] rows = new [] {"abc -4.01%", "def 6.45%", "monkey" };

foreach (string row in rows)
{
    //regex captures number but not %
    Match rownum = Regex.Match(row.ToString(), @"(\-?\d+\.+?\d+)%");

    //check for match
    if(!rownum.Success) continue;

    //get value of first (and only) capture
    string capture = rownum.Groups[1].Value;

    //convert to decimal
    decimal actual = decimal.Parse(capture);

    //TODO: do something with actual
}

edited Jun 13 '12 at 10:47

answered Jun 12 '12 at 10:43

WickyNilliams

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Correct me if I'm wrong, but doesn't "[^%]" mean that no `%` is allowed to follow the decimal string, but everything else is? – Franky Jun 12 '12 at 10:51
Correct, just copied the regex from above, thought to myself it was a bit iffy. I've updated the regex to match what he said his requirements were – WickyNilliams Jun 12 '12 at 11:00
Wicky, this makes perfect sense to me but is resulting in an FormatException was unhandled exception for the string act = rownum.Groups[1].Value; line. – user1442073 Jun 12 '12 at 11:12
Ah yes, this is where a value doesn't match the regex. See the changes i've made above, this should now handle unmatched values (added extra value "monkey" to array to prove this) – WickyNilliams Jun 12 '12 at 11:18
Well, the good news is I'm no longer getting any errors. The bad news is I'm not printing anything...? – user1442073 Jun 12 '12 at 11:22
If you create a test app which has exactly the code above (including the test array), doers it work? At this point I'm afraid it's just up to you and your debugger – WickyNilliams Jun 12 '12 at 11:24
Note, i've remove the code where you write to a textbox, there is no output from my solution, I'll leave that as an exercise for you :) – WickyNilliams Jun 12 '12 at 11:26
Yes, your code works perfectly. Hmm, I must have a bug on my end. With more coffee, I'm sure I can figure it out. Thanks a ton for your help :) – user1442073 Jun 12 '12 at 11:28
Coffee makes everything better. Good luck and thanks for accepting answer – WickyNilliams Jun 12 '12 at 11:42
1

just for the record: you should check the Match.Success property (i.e. rownum.Success) to see whether the expression actually matched anything before you continue with the group extraction – executor Jun 13 '12 at 06:07

score 1 · Answer 3 · answered Jun 12 '12 at 10:39

If you're going to use the Match class to handle this, then you have to access the Match.Groups property to get the collection of matches. This class assumes that more than one occurrence appears. If you can guarantee that you'll always get 1 and only 1 you could get it with:

string act = rownum.Groups[0];

Otherwise you'll need to parse through it as in the MSDN documentation.

C# Regex.Match to decimal

3 Answers3