Question

C# & ASP.NET

Create a console application that prompts the user to enter a regular expression, and then prompts the user to enter some input and compare the two for a match until the user presses Esc:

The default regular expression checks for at least one digit.
Enter a regular expression (or press ENTER to use the default): ^[a- z]+$
Enter some input: apples
apples matches ^[a-z]+$? True
Press ESC to end or any key to try again.
Enter a regular expression (or press ENTER to use the default): ^[a- z]+$
Enter some input: abc123xyz
abc123xyz matches ^[a-z]+$? False
Press ESC to end or any key to try again.

Answer 1

The Console program is given below. The comments are provided for the better understanding of the logic.

using System;
using System.Text.RegularExpressions;

public class Program
{
    public static void Main(string[] args)
    {
        string inputRegex = "";
        string inputString = "";

        //Display initial message
        Console.WriteLine("The default regular expression checks for at least one digit.");
        
        //Start a continuous loop.  The exit condition is taken care inside the loop.
        while (true)
        {
            //Read the regex pattern from the console.
            Console.Write("\nEnter a regular expression (or press ENTER to use the default): ");
            inputRegex = Console.ReadLine();
            //If Enter key is pressed, default the regex pattern to atleast 1 digit.
            if (inputRegex == "")
                inputRegex = "[0-9]+";

            //Read some input
            Console.Write("Enter some input: ");
            inputString = Console.ReadLine();

            //Check if the input matches the regex pattern entered.
            bool isMatchFound = Regex.IsMatch(inputString, inputRegex);

            //Display the message whether it matches or not.
            Console.WriteLine("{0} matches {1} ? {2}", inputString, inputRegex, isMatchFound);

            //Read a key from the user.
            Console.Write("\nPress ESC to end or any key to try again.");
            ConsoleKeyInfo key = Console.ReadKey();

            //If the Escape key is pressed, break the loop. Otherwise continue with the loop.
            if (key.Key == ConsoleKey.Escape)
                break;
        }
    }
}

The screenshots of the code and output are provided below.