Is there a way to understand a behaviour whether it's undefined-unspecified-implementation defined?   If we can't know, how can I avoid using these statements?  Also, if there is a source that I can find these kind of common UB's can you share?
What are all the common undefined behaviours that a C++ programmer should know about?  Say, like:  a[i] = i++;
On equations $m^2+1=5^n$ Correct usage of suspended hyphens I have seen some people using them while others not. Should I still use a suspended hyphen in the following snippet?     I have used upper- and lowercase in my script. Why is isNaN(null) == false in JS? This code in JS gives me a popup saying "i think null is a number", which I find slightly disturbing. What am I missing?    if (isNaN(null)) {   alert("null is not a number"); } else {   alert("i think null is a number"); }     I'm using Firefox 3. Is that a browser bug?  Other tests:    console.log(null == NaN);   // false console.log(isNaN("text")); // true console.log(NaN == "text"); // false     So, the problem seems not to be an exact comparison with NaN?  Edit: Now the question has been answered, I have cleaned up my post to have a better version for the archive. However, this renders some comments and even some answers a little incomprehensible. Don't blame their authors. Among the things I changed was:   Removed a note saying that I had screwed up the headline in the first place by reverting its meaning Earlier answers showed that I didn't state clearly enough why I thought the behaviour was weird, so I added the examples that check a string and do a manual comparison. How to use early stopping properly for training deep neural network? I have a deep neural network model and I need to train it on my dataset which consists of about 100,000 examples, my validation data contains about 1000 examples. Because it takes time to train each example (around 0.5s for each example) and in order to avoid overfitting, I would like to apply early stopping to prevent unnecessary computation. But I am not sure how to properly train my neural network with early stopping, several things I do not quite understand now:   What would be a good validation frequency? Should I check my model on the validation data at the end of each epoch? (My batch size is 1) Is it the case that the first few epochs might yield worse result before it starts converging to better value? In that case, should we train our network for several epochs before checking for early stopping? How to handle the case when the validation loss might go up and down? In that case, early stopping might prevent my model from learning further, right?   Thank you in advance. Drop In Reputation - But No Record Of Why? Illustrator Vector Graphics Appearing Pixellated Allow horizontal scrolling of long math expressions Stack Exchange formats math, but often the formatted math is wider than the screen. It would be nice if formatted math were scrollable the same way that formatted code wider than the screen is scrollable. I'm embarking on a journey to create a conference abstract book using XeTeX and got stuck within five minutes:        The missing 'g' in 'somethin' influences the line height of the following line. How can I correct this?  At the end I want to be able to include the abstracts and corresponding information through our online registration system, so this should be a global setting.  My MWE:  \documentclass[10pt, a5paper]{article} \usepackage{fontspec}  %% GEOMETRY \usepackage[left=2cm, right=1.5cm]{geometry} % to change the page dimensions  \newenvironment{AbsHead} {     \fontsize{16}{22}\headfont\noindent }% {     \vspace{0.5 cm} }  \newenvironment{AbsAuthors} {     \fontsize{12}{14}\authorfont\noindent }% {    \vspace{0.5 cm} }  \begin{document}  ￼￼￼￼\setmainfont{Minion Pro} \newfontfamily\authorfont{Helvetica Neue Light} \newfontfamily\headfont{Helvetica Neue Condensed Bold}  \begin{AbsHead}The XIAP  something something something somethin somethin somethin somethin somethin somethin somethin something something\end{AbsHead}   \begin{AbsAuthors}Somebody Someone\end{AbsAuthors}   \noindent Purpose: Lorem ipsum \end{document} Pixelated image in ps format! I'm trying modeling things like this using oracle:  An account can have 1~5 members  So I'll have a account table and a member table with a FK of account. But is that possible to check if the account have less than 5 members?  I've tried constraint and trigger but oracle doesn't allow sub queries in constraint or condition of trigger like  CHECK( SELECT ...) or IF count(*) &gt;= 5  which make things getting hard. Unable to start XAMPP using sudo in Desktop Entry (p.236)  has a proof that the equation $e^z-z=0$ has infinitely many complex solutions:    I'm curious if there are any particularly elegant ways to see this, other than that given in the text. I'm sure there must be a simple reason for this but I can't seem to be able to import a shp file or a feature class from another file or sde geodatabase into a Feature Dataset without getting an error.  The feature classes come in fine if I don't don't try to import them into a Feature Dataset.  The feature dataset definitely has the same projection as the feature classes I'm trying to import so I don't think that's the problem.  The Error I get is ERROR 000210 and just says Failed to convert and cannot create output and Failed to execute (CopyFeatures).    Any ideas what I may be doing wrong here.  Seems like something so simple.  I'm trying to use the Feature Datasets to better organize my data which I think is there purpose.   Update:  So as you can see below, Jason helped me find the answer.   As suggested by Matt below, I added a new Idea to the ArcGIS Ideas site.  Here is the link to that, so please promote this up if you agree a better error message is needed here: Using a singular or plural verb after "and/or" If the subject of a sentence is separated by "and/or", should the verb be pluralized, as with "and", or agree with the rightmost subject, as with "or"? For example:     His co-workers and/or his boss was at fault.   vs.     His co-workers and/or his boss were at fault. Polynomial in $n$ variables Let $f$ be polynomial in $n$ variables. If we have $f(a_1,\ldots,a_n) = 0, a_i \in S_i$ and $S_1,\ldots,S_n$ are infinite subsets of a field $k$, how can I show that $f=0$? I'm using uninstall.php for my plugin to delete all the traces my plugin did to a site on uninstall (delete). I did it in a good way, but even after the deletion there are some fields in the options table:   uninstall_plugins recently_activated _site_transient_update_plugins   in these options there are multiple values from other plugins too.  How can I take care of such traces, how can I remove all those traces too?  I checked WooCommerce and found they leave no traces after there deletion, if the "delete data" checkbox is checked.  How can I do so? Proof that a sequence is convergent I'm asked to prove the convergence of the sequence $$X_n=\left(1+\frac12\right)\left(1+\frac14\right)\left(1+\frac18\right)\cdots\left(1+\frac{1}{2^n}\right)$$   I proved that it is increasing through the ratio test and then I want to prove that it is bounded.  My question is the following : is it enough to say that $X_n&lt;\left(\frac32\right)^n$ for $n&gt;1$ or not ? Namely, can we say that a sequence is bounded if $\forall$  $n$ ,  $\exists$ a $N$ such that $X_n&lt;N$ or do I have to find a N such that $\forall$  $n$ , $X_n&lt;N$?  In other words, can a bound depend on $n$ ?  Thanks for your help. Is it OK to crosspost Stack Overflow questions, now that the Portuguese SO is open? How to rename file as below  AS1100801000002.RAW7AGS  AS1100801001008.RAW7AH4 AS1100801002001.RAW7AH9 AS1100801003002.RAW7AHE AS1100801004009.RAW7AHT AS1100801005002.RAW7AHY AS1100801010002.RAW7AJ3   to new name  AS1.txt AS2.txt AS3.txt AS4.txt AS5.txt AS6.txt AS7.txt I am trying to solve the following exercise:     Prove that complex multiplication does not extend to a multiplication   on $\mathbb R^3$ so as to make $\mathbb R^3$ into a real division   algebra.   I am aware of Frobenius' theorem that there are only three finite dimensional real associative division algebras. But the exercise would be pointless if the theorem was assumed.   Let $x,y \in \mathbb R^3$. Since $x y$ has to extend the complex multiplication:  $$xy = (x_1y_1-x_2y_2, x_1y_2 + x_2 y_1, ?)$$  I have no idea how I can proceed from here. Could someone tell me how to do this? It should be easy as the other exercises I did so far were also easy.