Question

I’m trying to come up with a lightning fast solution to find portions in a string. Here is a Sample string:

“PostLoad successful! You transferred amount of 17.00 Rs to 03334224222. Now use PostLoad by dialing 123. PostLoad on SMS will end on 01-03-2011.”

Objective: Need to retrieve the bold values: Amount and Cell Number. The string contents change slightly but the cell number will always be a 11 digit. The amount is always with two decimal precision. Any suggestions using C# and RegEx?

Answer 1

Regex regexObj = new Regex(@"(\b\d+\.\d{2}\b).*?(\b\d{11}\b)");
Match matchResults = regexObj.Match(subjectString);
while (matchResults.Success) {
    for (int i = 1; i < matchResults.Groups.Count; i++) {
        Group groupObj = matchResults.Groups[i];
        if (groupObj.Success) {
            // matched text: groupObj.Value
            // match start: groupObj.Index
            // match length: groupObj.Length
        } 
    }

Explanation:

(       # Match and capture the following:
 \b     # Assert that the match starts at a "word boundary"
 \d+    # Match one or more digits
 \.     # Match a .
 \d{2}  # Match exactly two digits
 \b     # Assert that the number ends here
)       # End of first capturing group
.*?     # Match any number of intervening characters; as few as possible
(       # Match and capture...
 \b     # Word boundary
 \d{11} # Exactly 11 digits
 \b     # Word boundary
)       # End of match

Group #1 will contain the decimal number, group #2 will contain the 11-digit number.

A “word boundary” is the position between an alphanumeric character and a non-alphanumeric character, so it only matches at the start or end of a “word or number”.

This ensures that numbers like 12.3456 will not be matched; on the other hand, it is necessary for the numbers to be delimited by whitespace, punctuation or other non-alnum characters. For example, in number12.34 the regex would not match 12.34.