C# Regular Expression

In C#, a regular expression (or regex) is a pattern that specifies a set of strings. Regular expressions are used to validate input, search for patterns, and replace text in a string. In this tutorial, we'll discuss how to use regular expressions in C#.

Syntax

The syntax for defining a regular expression in C# is as follows:

Regex regex = new Regex(pattern);

The pattern parameter is the regular expression string that defines the pattern you want to match.

Example

Let's say we want to validate a phone number input in a C# program. We can use a regular expression to ensure that the phone number is in the correct format. Here's how we can implement it:

using System;
using System.Text.RegularExpressions;

class Program {
    static void Main(string[] args) {
        string phoneRegex = @"^\d{3}-\d{3}-\d{4}$";
        Regex regex = new Regex(phoneRegex);

        Console.WriteLine("Enter phone number (XXX-XXX-XXXX):");
        string input = Console.ReadLine();

        if (regex.IsMatch(input)) {
            Console.WriteLine("Valid phone number");
        } else {
            Console.WriteLine("Invalid phone number");
        }
    }
}

Now, we can enter a phone number and the program will validate it using the regular expression pattern.

Output

When we run the example code above and enter a valid phone number (e.g. 123-456-7890), the output will be:

Valid phone number

If we enter an invalid phone number (e.g. 1234567890), the output will be:

Invalid phone number

Explanation

In the example above, we defined a regular expression pattern that matches phone numbers in the format XXX-XXX-XXXX. We then created a Regex object using the pattern and used it to validate user input in a C# console application.

Use

Regular expressions can be used in a variety of ways in C#, such as to validate input, search for patterns, and replace text in a string. They are useful for tasks such as form validation, data filtering, and text processing.

Important Points

• Regular expressions are case-sensitive by default, but you can use the RegexOptions.IgnoreCase option to make them case-insensitive.
• The ^ and $ characters in a regular expression denote the beginning and end of a string, respectively.
• The \d character in a regular expression matches any digit, and the {n} syntax matches n instances of the preceding expression.

Summary

In this tutorial, we discussed how to use regular expressions in C# to validate phone numbers. We covered the syntax, example, output, explanation, use, and important points of regular expressions in C#. With this knowledge, you can now use regular expressions in your C# code to validate input, search for patterns, and replace text in a string.