Tutorial: C# Regex

#1
Guest_NeedHelp_*

Posted 28 June 2006 - 08:27 AM

Guests

I figured I would write this little tutorial about C# and Regex since it is still fresh in my mind.

The code below shows how to remove all spaces from a string:


using System;

using System.Collections.Generic;

using System.Text;


namespace regexconsole

{

    class Program

    {

        static void Main(string[] args)

        {

            // Create a string and display it to the console

            string display = "I have     several   spaces in me";

            Console.WriteLine(display);


            // Replaces all spaces with 1 space

            display = System.Text.RegularExpressions.Regex.Replace(display," +", " ");

            Console.WriteLine(display);


            // Make it pause

            Console.ReadLine();


        }

    }

}

Here is how to determine if a string is a number or not


using System;

using System.Collections.Generic;

using System.Text;


namespace regexconsole

{

    class Program

    {

        static void Main(string[] args)

        {

            // Create an integer and display it

            string number = "64";

            Console.WriteLine(number);


            // Determine if it is a positive number

            if (System.Text.RegularExpressions.Regex.IsMatch(number, ("[0-9]*")))

            {

                Console.WriteLine("This is a number");

            }

            else

            {

                Console.WriteLine("This is not a number!");

            }




            // Make it pause

            Console.ReadLine();


        }

    }

}

That is it for now. I will post more later.

#2
bassio

Posted 01 May 2007 - 03:25 AM

Newbie

Members
2 posts

thanks alot man, really nice.

#3
v0id

Posted 01 May 2007 - 03:44 AM

Retired

Members
2,936 posts

It would be nice if you could tell something about regular expressions, and how they works, for those people there doesn't know what it actually is.
I wouldn't call this a tutorial, it had been better with, "Examples" or something.

#4
bishisht

Posted 28 June 2010 - 12:06 AM

Newbie

Members
23 posts

v0id said:

It would be nice if you could tell something about regular expressions, and how they works, for those people there doesn't know what it actually is.

yes for the people like me it would be wonderful if you place some tutorial on regular expressions

#5
Kai_it

Posted 23 July 2010 - 06:06 AM

Newbie

Members
7 posts

i'm rewrite follow your tut, but it show incorrect.

Posted Image

are you sure write correct this code?

sr i'm not not fluent English. I'm from Vietnam

#6
wim DC

Posted 23 July 2010 - 06:34 AM

Writes binary right handed and hex left handed

Members
2,084 posts

The author of this tutorial hasn't been active anymore since 2008.

What's wrong with it? The screenshot tells me that it's working correct. I mean 55 IS a number...

#7
bishisht

Posted 23 July 2010 - 09:21 AM

Newbie

Members
23 posts

yeah the second code piece has a bug in it...it always show "This is a number" or a kinda that even when you enter a piece of text

#8
Kai_it

Posted 24 July 2010 - 01:20 AM

Newbie

Members
7 posts

oxano said:

The author of this tutorial hasn't been active anymore since 2008.

What's wrong with it? The screenshot tells me that it's working correct. I mean 55 IS a number...

but i'm type "xyz" then messengerbox show "this is a number. I don't know author of this tutorial hasn't been active

bishisht said:

yeah the second code piece has a bug in it...it always show "This is a number" or a kinda that even when you enter a piece of text

You've found the problem

p/s: this is nice tutorial

#9
wim DC

Posted 24 July 2010 - 02:59 AM

Writes binary right handed and hex left handed

Members
2,084 posts

Oh didn't see the right part of your screenshot when i posted that...

Yes in the second part of his code you must replace

string number = "64";

by user input or something.

The regex seems correct
[0-9] -- means: a character between and including 0 and 9
* -- means: 0,1 or more times

So if the string you give has only characters between 0 and 9, it'll validate.

for letters there is a difference in case and you can't do [a-Z] because it'll validate a bunch of extra stuff too. It uses the ascii table and you'll see that the range a-Z will be wrong: Ascii Table - ASCII character codes and html, octal, hex and decimal chart conversion

#10
Kai_it

Posted 24 July 2010 - 08:00 AM

Newbie

Members
7 posts

i'm tried "string number = "64";" as author's code, but it always show "This is a number"

#11
wim DC

Posted 24 July 2010 - 08:34 AM

Writes binary right handed and hex left handed

Members
2,084 posts

Could you show us the code you're using? (in code tags, click the # button )

#12
Kai_it

Posted 24 July 2010 - 09:46 AM

Newbie

Members
7 posts

same author's code

string number = txtInput.Text;

            if (System.Text.RegularExpressions.Regex.IsMatch(number, ("[0-9]*")))

            {

                MessageBox.Show("This is a number");

            }

            else

            {

                MessageBox.Show("This is not a number");

            }