C# Regex and email format This is not working as I intended it to, regardless it's running my if clause even if my email format is: something like hello@gmail.com not sure what is wrong here.          Regex RX = new Regex("^[a-zA-Z0-9]{1,20}@[a-zA-Z0-9]{1-20}.[a-zA-Z]{2,3}$");         if (!RX.IsMatch(textEmail.Text))         {             MessageBox.Show("Email format is not correct");         }          else         {             MessageBox.Show("Email format is CORRECT");         }   it should really run the else clause
How to validate an email address using a regular expression? Over the years I have slowly developed a  that validates MOST email addresses correctly, assuming they don't use an IP address as the server part.  I use it in several PHP programs, and it works most of the time.  However, from time to time I get contacted by someone that is having trouble with a site that uses it, and I end up having to make some adjustment (most recently I realized that I wasn't allowing 4-character TLDs).  What is the best regular expression you have or have seen for validating emails?  I've seen several solutions that use functions that use several shorter expressions, but I'd rather have one long complex expression in a simple function instead of several short expression in a more complex function.
Why does:   $$ \sum_{k=0}^{n} k \binom nk p^k (1-p)^{n-k} = np $$ ? Taking the derivative of:   $$ \sum_{k=0}^{n}  \binom nk p^k (1-p)^{n-k} = (1 + [1-P])^n = 1 $$   does not seem useful, since you would get zero. And induction hasn't yet worked for me, since – during the inductive step – I am unable to prove that:   $$ \sum_{k=0}^{n+1} k \binom {n+1}{k} p^k (1-p)^{n+1-k} = (n+1)p  $$   assuming that:   $$ \sum_{k=0}^{n} k \binom {n}{k} p^k (1-p)^{n-k} = np  $$ Any javascript event occurring when user clicks Stop load button? How to create two classes in C++ which use each other as data? Difference between $(this) and event.target? I have dual boot configured with Windows 7 (32bit) and Ubuntu 12.04(64bit). I installed Ubuntu after windows, now my windows is corrupt due to some virus and I need to reinstall it. Currently when I start my PC, grub loader comes up and I need to select Ubuntu or Windows.   I was wondering how can I install windows again and still have my Ubuntu install? Is there a way to do this?  I do not want to install Ubuntu again and lose my settings and data there.   Thanks, Ketan Evaluating a PDF to find an unkown constant Evaluate the PDF to find K  $1 = \int_0^{\infty} \frac{k}{(1+x)^4}$  using u substitution I got:  $u=1+x$ and $du= dx$  $\int_0^{\infty} \frac{k}{u^4} \to \frac{k}{\frac{-1}{3} u^3}$   Since $u^4 du = \frac{u^{-4+1}}{-4+1}=$ $\frac{u^{-3}}{-3}$  which evaluating gives:  $1=\frac{k}{\frac{-1}{3(1+x)^3}} \vert_0^{\infty} \to \frac{-3k}{(1+x)^3} \vert_0^{\infty} = 0 -3k$   and $k= \frac{-1}{3}$  somehow though they came up with $\frac{-k}{3} \frac{1}{(1+x)^3}$ after integrating $\int_0^{\infty} \frac{k}{(1+x)^3}$   Was my approach correct to use substitution? Where does my work go wrong? Load Excel data sheet to Oracle database I am looking for a free tool to load Excel data sheet into an Oracle database. I tried the Oracle SQL developer, but it keeps throwing a NullPointerException. Any ideas? Experimental observation of matter/antimatter in the universe Ordinary matter and antimatter have the same physical properties when it comes to, for example, spectroscopy. Hydrogen and antihydrogen atoms produce the same spectroscopy when excited, and adsorb the same frequencies. The charge does not make a difference in the potential (regardless if it's generated by a proton or an antiproton) nor in how the positron behaves in this potential (being its mass equal to the mass of an electron)  How can astronomy evaluate if a far galaxy is made of matter or antimatter, given that from the spectroscopy point of view, they behave in the same way? In other words, how do we know that an asymmetry exists between matter and antimatter in the universe? Style Guide: Bold, Italic, or Quotes When I Want to Emphasize Something Let’s say I have many lists of this kind on a page:   Click on the Foo button. Tick the Bar box. Click on the Save button.   How should I emphasize Foo, Bar, and Save?   Bold?   Click on the Foo button. Tick the Bar box. Click on the Save button.  Italic?   Click on the Foo button. Tick the Bar box. Click on the Save button.  Quotes?   Click on the “Foo” button. Tick the “Bar” box. Click on the “Save” button.    NOTE: I want the lists to be read as easy as possible. So, the question pretty much says it all. I'm on Snow Leopard, and I do a lot of web development, particularly in Rails 3 which makes heavy use of the console.  I've seen some notable bloggers etc. mention Zsh as their preference over Bash, but I don't know what difference it would make.  Could anyone give me a good comparison of what difference there is and what might make one prefer one option or the other? How can I find out which app is putting ads in my notification bar? Possible Duplicate:          Recently advertisements have started appearing as notifications in my phone's notification bar. The icon on the ad are either a green plus sign or a white star with a red circle inside it. There is no indication in the notification as to which app it came from.  I haven't installed any new applications, so I assume that some application updated to include this intrusive new ad system. Ads only show up at irregular intervals once every few hours, so removing all my apps one by one until the ads stop is not really a viable option, since I would have to wait several hours in between each uninstall to see if another ad appears. (I'm sure this is by design.)  So is there any way to figure out the source application of these notification ads?  My phone is a rooted/unlocked/whatever HTC Droid Incredible running MIUI. Food in the Star Wars Universe? Could a constant function be considered increasing? Given the definition of an increasing function as a function $f:E\to\mathbb{R}$, where $E$ is nonempty such that $x_1,x_2\in E$ and $x_1&lt;x_2$ imply $f(x_1)\leq f(x_2)$, then couldn't, for example, $f(x)=-1$ considered increasing? Since the inequality is not a strict inequality. How to modify the space between the numbers and text of sectioning titles in the table of contents? Why didn't (or did) I or some other user get a hat although the requirements were (or weren't) fulfilled? During Winter Bash, users can earn hats. But sometimes it seems that a hat was awarded even though its requirements weren't (yet) met, or vice versa.  What could be the reason for this? How to convert wstring into string? I have the formula $x! + y! = z!$ and I'm looking for positive integers that make it true. Upon  inspection it seems that x = y = 1 and z = 2 is the only solution. The problem is how to show it.   From the definition of the factorial function we know $x! = x(x-1)(x-2)...(2)(1)$  So we can do something like this:  $$ [x(x-1)(x-2)...(2)(1)] + [y(y-1)(y-2)...(2)(1)] = [z(z-1)(z-2)...(2)(1)]$$   we can then factor all of the common terms out on the LHS.  $$ [...(2)(1)][x(x-1)(x-2)... + y(y-1)(y-2)...] = [z(z-1)(z-2)...(2)(1)]$$ and divide the common terms out of the right hand side  $$[x(x-1)(x-2)...] + [y(y-1)(y-2)...] = [z(z-1)(z-2)...]$$  I'm stuck on how to proceed and how to make a clearer argument that there is only the one solution (if indeed there is only the one solution).   If anybody can provide a hint as to how to proceed I would appreciate it. Modifying cat command to number paragraphs and display last paragraph only I have a text file for which I need to do three things:   Modify the "cat" command to highlight keywords whilst showing the complete contents of the file.  Modify the "cat" command to automatically number the paragraphs. These are separated by a single blank line.  Modify the "cat" command to display the final paragraph only.    The tricky part is that all of these need to be done by modifying the cat command.   I've seen many forum posts explaining that cat is not meant for this - and I can entirely see why. However, the challenge is that I have to use cat! Change the size/width of tabs in Notepad++ $\sum_{n=1}^\infty\frac{z^n}{n}$ does not converge uniformly on $\mathbb{D}$. It is required to prove that the series $\sum_{n=1}^\infty\frac{z^n}{n}$ does not converge uniformly on the open unit disc centered at $0$, i.e. $\mathbb{D}$. Clearly by virtue of the ratio test the series converges pointwise on  $\mathbb{D}$. However I find it difficult to see why the convergence is not uniform. Could someone please give me a hint?