Round #884

Write a Regex that matches IPv4 addresses in the form '1.2.3.4' (each octet 0–255). Use Regex.Match on a sample string.

```csharp using System; using System.Text.RegularExpressions; class Program { static void Main() { // Sample string string sampleString = "The IP address is 192.168.1.1"; // Regex pattern for IPv4 address string pattern = @"\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b"; // Search for IP address in the sample string Match match = Regex.Match(sampleString, pattern); if (match.Success) { Console.WriteLine("IP address found: " + match.Value); } else { Console.WriteLine("No IP address found"); } } } ```

```csharp using System.Text.RegularExpressions; public class Program { public static void Main() { // Regex pattern to match IPv4 addresses string pattern = @"^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$"; // Sample string string sampleString = "The IP address is 192.168.1.1"; // Use Regex.Match to find the first occurrence of the pattern in the sample string Match match = Regex.Match(sampleString, pattern); if (match.Success) { System.Console.WriteLine("IPv4 address found: " + match.Value); } else { System.Console.WriteLine("No IPv4 address found"); } } } ``` This code defines a regex pattern to match IPv4 addresses and uses `Regex.Match` to find the first occurrence of this pattern in a sample string. The pattern `^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$` breaks down into four parts, each matching a number between 0 and 255, separated by dots. The `^` and `$` anchors ensure that the entire string must match this pattern, not just a part of it. This implementation genuinely requires more text to explain the regex pattern and its usage.