A way to determine type of derived class with minimum code in c++
What is object slicing?
I was speaking to an English learner and said, “All you have to do is read a lot.” And they thought that sentence wasn’t grammatically correct because I dropped the word to between is and read.  They thought it should be “All you have to do is to read a lot.” That sounds weird to me.   How do I explain to them the reason you drop the to? Or am I incorrect and it really should have a to? Would Gravitational Time Dilation still apply between two gravitational sources? As explained on , when an object is experiencing strong gravitational forces, time passes slower for it. If, in theory, you had two objects exerting the same amount of gravitational pressure on an object in opposite directions, effectively cancelling each other out, would they cancel out the time dilation, or would they compound, making the time dilation more prevalant? Chrome and Firefox cannot add specific URL to home screen Out-of-control starship results in some crew members landing in a rebirthed universe? Order of finite fields is $p^n$ Why is there an electric field in a wire even though it is a conductor? If you take a perfect conductor, there cannot be a field across it since if there were, the particles would arrange themselves in a way to cancel out the field right?  Yet, why does the same not hold true for a wire. A wire is essentially a long, thin conductor yet electrons do indeed flow so there must be an electric field.  Does this not contradict with what happens in a conductor? Why don't the electrons re-arrange to cancel out the electric field? Gaps between arrows and labels Passing HTML to template using Flask/Jinja2 How can I make Ubuntu 18.04 / 18.10 desktop use Unity (be like Ubuntu 14.04)? If I push or hit an object in space will it rotate or move along a straight line? Why is Harry Potter a half-blood? Being born to James and Lily, how can Harry be called a half-blood?  It is said that admission in Hogwarts is given to children of Muggles when they show magical talents as a child, and Lily was no exception to this. This makes Lily a witch, so why is Harry half-blooded? Number of moves necessary to solve Rubik's cube by pure chance Suppose, random moves are made to solve Rubik's cube. A move consists of a $90$-degree-rotation of some side. The starting position is also random.   What is $E(X)$, where $X$ is the number of moves until the cube is solved ? How many moves must be made, that the probability that the cube is solved, exceeds $99$% ? I am wondering if my proof is correct? Thank you for whoever willing to take a look at it for me.     Proof $\liminf E_k \subset \limsup E_k $   If $\{E_k\}_{k=1}^\infty$ is a sequence of sets, we define \begin{align*} \limsup E_k &amp; = \bigcap_{j=1}^\infty\left(\bigcup_{k=j}^\infty E_k\right)\\ &amp;= \bigcap_{j=1}^\infty(E_j \cup E_{j+1} \cup \cdots)\\ &amp;= (E_1 \cup E_2 \cup \cdots) \cap (E_2 \cup E_3 \cup \cdots) \cap \cdots. \end{align*}  Therefore, $\limsup E_k$ consists of those points in $\mathbb{R}^n$ which belong to infinitely many $E_k$. \begin{align*} \liminf E_k &amp; = \bigcup_{j=1}^\infty\left(\bigcap_{k=j}^\infty E_k\right)\\ &amp;= \bigcup_{j=1}^\infty(E_j \cap E_{j+1} \cap \cdots)\\ &amp;= (E_1 \cap E_2 \cap \cdots) \cup (E_2 \cap E_3 \cap \cdots) \cup \cdots. \end{align*} Therefore, $\liminf E_k$ consists of those points in $\mathbb{R}^n$ which belong to all $E_k$ for $k \geq k_0$.  Now consider $x \in \liminf E_k$, then $x \in E_1 \cap E_2 \cap \cdots$, or $x \in E_2 \cap E_3 \cap \cdots$ and so on, that is to say, $x \in E_{k_0} \cup E_{k_0+1} \cup \dots$ for some $k_0$. More specifically, $x \in E_k \forall k \geq k_0$. Therefore, $x \in (E_1 \cup E_2 \cup \cdots) \cap (E_2 \cup E_3 \cup \cdots) \cap \cdots$, so we showed $x \in \limsup E_k$. How can I contribute to Ubuntu? I would like to know what kinds of contributions someone can make to Ubuntu. Such as Programmer, User, Proofreader, etc. With the listings package, I would like to color the integers out of strings and comments and out of keywords too. The question for coloring numbers     . Some answer handle the numbers occurring within comments, strings or barewords, but no solution given work when a keyword contain a number. Which is annoying because C and C++ have a lot of types with a number in them, like uint32_t.  Here is a small example.  \documentclass{standalone} \usepackage{xcolor} \usepackage{listings}  \definecolor{darkgreen}{rgb}{0.18,0.54,0.34} \definecolor{maroon}{rgb}{0.64,0.16,0.16} \definecolor{darkpink}{rgb}{0.75,0.25,0.5}  \lstdefinestyle{myc++}{     language=[ISO]C++,     keywordstyle=\color{darkgreen}\bfseries,     commentstyle=\color{blue}\textit,     stringstyle=\color{darkpink}\ttfamily, %     literate=*     {0}{{{\textcolor{red}0}}}1     {1}{{{\textcolor{red}1}}}1     {2}{{{\textcolor{red}2}}}1     {3}{{{\textcolor{red}3}}}1     {4}{{{\textcolor{red}4}}}1     {5}{{{\textcolor{red}5}}}1     {6}{{{\textcolor{red}6}}}1     {7}{{{\textcolor{red}7}}}1     {8}{{{\textcolor{red}8}}}1     {9}{{{\textcolor{red}9}}}1,     escapeinside={|}{|}, %     morekeywords={int32_t} }  \begin{document}  \begin{lstlisting}[style=myc++] // In comment: 42 int32_t in_keyword = 80085; char *in_identifier|2| = "And in string 1337\n"; \end{lstlisting}  \end{document}   And the result:    The star for literate avoid to coloring the digits inside comments or strings. The escapeinside avoid coloring the digits inside a bareword when specifically marked. But I have yet to find how to color int32_t as a keyword. In the Linux system, we can use bellow command to enable packets forwarding:  ~ # sysctl net.ipv4.ip_forward=1 net.ipv4.ip_forward = 1   but how can I realize the same function in Windows?  I use Windows Server 2008 R2. 'pyrcc4' is not recognized as an internal or external command? C:\Users\Department\.qgis2\python\plugins\np&gt;pyrcc4 -py2 resources.qrc -o resources.py      'pyrcc4' is not recognized as an internal or external command,      operable program or batch file.   How do I solve this problem? How accurate is the GPS on the iPhone's Find My iPhone app?  I used Find My iPhone app to track a friend. The first 3 stops were dead on but when it refreshed it showed them to be several streets over from actual location. What could cause that? How do I downgrade Minecraft to play on a server running an older version? I am wondering, given the minimal polynomial of $A$, what can we say about the minimal polynomial of $A^n$?  I know that if we were looking at the roots of the characteristic polynomial ie eigenvalues then the roots of the characteristic polynomial of $A^n$ would be $nth$ powers of the eigenvalues so again these are roots of the minimal polynomial also.