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After a long break, Eric is back, and continue his awesome Regex 101 Exercise series, in this exercise, the question Eric asks is:
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Given a string like:

# # 4 6 # # 7 # 45 # 43 # 65 56 2 # 4345 # # 23

Count how many numbers there are in this string

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I have three simple solutions to this problem.
Solution #1:
Regex regex = new Regex(@"\d+", RegexOptions.IgnoreCase);
String inputString
= @"# # 4 6 # # 7 # 45 # 43 # 65 56 2 # 4345 # # 23";
Int32 count
= 0;
regex.Replace(inputString,
delegate(Match match)
{
count
++;

return String.Empty;
});

Console.WriteLine(count);

Solution
#2:
Regex regex = new Regex(@"\d+", RegexOptions.IgnoreCase);
String inputString
= @"# # 4 6 # # 7 # 45 # 43 # 65 56 2 # 4345 # # 23";
MatchCollection matches
= regex.Matches(inputString);
Console.WriteLine(matches.Count);

Solution
#3:
Regex regex = new Regex(@"[#\s]+", RegexOptions.IgnoreCase);
String inputString
= @"# # 4 6 # # 7 # 45 # 43 # 65 56 2 # 4345 # # 23";
String[] values
= regex.Split(inputString);
Console.WriteLine(values.Length
- 1);

Side note: For all of you who are interested in regluar expressions, and want to be more proficient at it, I encourage you to actively participate in Eric Gunnerson's regex exercises, at the end of day, you will find that you benefit a lot in that process.