using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @"(?<!\d[\s-])(?<!\d)4\d{3}(?![\s-]?\d)";
string input = @"For example: 4567 (match)
I have 4999 roses (match)
1234567 days are gone (no match)
My water supply account is 123 4567 89 (no match)
Howdy, my cell number is 123-4567-89 (no match)
no match for 123 4567";
RegexOptions options = RegexOptions.Multiline;
foreach (Match m in Regex.Matches(input, pattern, options))
{
Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index);
}
}
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx