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Pattern Matching with Regular Expressions

Pattern Matching with Regular Expressions

Learn about regular expressions to validate user input, understand their syntax, and efficiently use them for tasks like splitting complex comma-separated strings.

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Regular expressions are useful for validating input from the user. They are very powerful and can get very complicated. Almost all programming languages support regular expressions and use a common set of special characters to define them. Let’s try out some example regular expressions:

Step 1: Use your preferred code editor to add a new Console App or console project named WorkingWithRegularExpressions to the Chapter08 solution or workspace:

  • In Visual Studio Code, select WorkingWithRegularExpressions as the active OmniSharp project.

Step 2: In Program.cs, delete the existing statements, and then import the following namespace:

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using System.Text.RegularExpressions; // Regex

Checking for digits entered as text

We will start by implementing the common example of validating number input:

Step 1: In Program.cs, add statements to prompt the user to enter their age and then check that it is valid using a regular expression that looks for a digit character, as shown in the following code:

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Write("Enter your age: ");
string input = ReadLine()!; // null-forgiving
Regex ageChecker = new(@"\d");
if (ageChecker.IsMatch(input))
{
  WriteLine("Thank you!");
}
else
{
  WriteLine($"This is not a valid age: {input}");
}

Note the following about the code:

  • The @ character switches off the ability to use ...