I am checking a student's homework. The assignment is to print the amount of English letters to the console. For some reason, what he did works (7th line):   int main(void)  {      char first = 'A';      char last = 'Z';      int amount = 0;       amount = ("%d - %d", last - first + 1);      printf("The amount of letters in the English alphabet is %d\n", amount);       return(0);  }   After seeing it, I tried putting other things in the brackets instead of "%d - %d". No matter what I put there and how many commas were there, it'd only take what's after the last comma (which is the correct sentence).  What is actually happening there?
What does the , operator do in C?
Indefinite integral of $ \int \frac{x^3}{\sqrt{x^2+1}} \,\text{d}x$. Can you please provide any sort of hint or suggestion on how to find the following indefinite integral?  $$\int\frac{x^3}{\sqrt{x^2+1}}\text{d}x$$  I tried substituting everything but it didn't work. I also tried trigonometric substitution but I couldn't find any valid trigonometric identity for $ \sqrt{\cos^2(x)+1} $ or $ \sqrt{\sin^2(x)+1} $. Anyone know if R has quote-like operators like Perl's qw() for generating character vectors? How did Enrico Fermi calculate the classical Fermi Problem? From Wikipedia: Fermi was known for his ability to make good approximate calculations with little or no actual data, hence the name. One example is his estimate of the strength of the atomic bomb detonated at the Trinity test, based on the distance travelled by pieces of paper dropped from his hand during the blast. Fermi's estimate of 10 kilotons of TNT was remarkably close to the now-accepted value of around 20 kilotons, a difference of less than one order of magnitude.  I have not been able to find any references explaining how he made this calculation. Please provide a reference or an example calculation.  See also: How to pick the title of a remote webpage Python and regular expression with Unicode I need to delete some Unicode symbols from the string 'بِسْمِ اللَّهِ الرَّحْمَٰنِ الرَّحِيمِ'  I know they exist here for sure. I tried:  re.sub('([\u064B-\u0652\u06D4\u0670\u0674\u06D5-\u06ED]+)', '', 'بِسْمِ اللَّهِ الرَّحْمَٰنِ الرَّحِيمِ')   but it doesn't work. String stays the same. What am I doing wrong? Class imbalance strategies When dealing with the class imbalance problem in a binary classifier, there are three ways I know of to address it: over-sampling, under-sampling and using cost-sensitive methods.   Are there any guidelines, rules of thumb or general strategies to choose among these methods? A possible answer would be: over-sample when the positive class has more than 100 instances (I just made it up). I have noticed that I hardly ever use the \negthinspace command  \!.  This is because I don't know how to use it properly (I do use other spacing commands quite a bit, because I can better understand the guidelines of when they might be useful). When might it be considered appropriate to use this spacing command? Visual design changes to the review queues How do I get a list of installed files from a package? How can I dual boot Windows and Ubuntu? Does opacity:0 have exactly the same effect as visibility:hidden If so, does it effectively deprecate the visibility property?  (I realize that Internet Explorer does not yet support this CSS2 property.) Disk storage graphic and usage amount inconsistent? 32-bit vs. 64-bit systems Subject–verb agreement not clear in "Is two bars OK?" Is the following correct?     Can I get some chocolate for myself? Yes, you can but not much.   Is two bars OK?   Is there any rule to explain the sentence above?  The dialogue's taken from Grammar Textbook Round-Up Level #3. If $U_1$, $U_2,\ldots,U_n$ are proper subspaces of a vector space $V$ over a field $F$, and $|F|\gt n-1$, why is $V$ not equal to the union of the subspaces $U_1$, $U_2,\ldots,U_n$? How can I find $\gcd(a^m+1,a^n+1)$ with $a,m,n$ positive integers? How can I find $\gcd(a^m+1,a^n+1)$ with $a,m,n$ positive integers?    I have this idea:  Let $d=\gcd(m,n)$. Then there exist positive integers $x,y$ such that $mx-ny=d$ (WLOG). We shall find $G=\gcd(a^m+1,a^n+1)$.  If $m,n$ are odd, then $d$ is odd, therefore one and only one of $x,y$ is even. We have:  $$a^{ny}(a^d+1)=a^{mx}+a^{ny}=(a^{mx}-1)+(a^{ny}+1)=(a^{mx}+1)+(a^{ny}-1).$$  If $x$ is even and $y$ is odd, then $a^{m}+1\mid a^{mx}-1$ and $a^{n}+1\mid a^{ny}+1$, therefore $G\mid a^{ny}(a^d+1)$. If $x$ is odd and $y$ is even, then $a^{m}+1\mid a^{mx}+1$ and $a^{n}+1\mid a^{ny}-1$, thus $G\mid a^{ny}(a^d+1)$. However, since $\gcd(a^m+1,a^{ny})=\gcd(a^n+1,a^{ny})=1$, so $\gcd(G,a^{ny})=1$, hence $G\mid a^d+1$. We also have $a^d+1\mid a^{m}+1$ and $a^d+1\mid a^{n}+1$, so $a^d+1\mid G$. Thus $G=a^d+1$.  If $v_2(m)=v_2(n)=v_2(d)=k&gt;1$, then there exist some odd numbers $m_1,n_1,d_1$ such that $m=2^km_1,n=2^kn_1,d=2^kd_1$. We shall have $m_1x-n_1y=d_1$, so one and only one of $x,y$ is even, and we can use the same argument when $m,n$ are odd, so $G=a^d+1$.  However, if $v_2(m) \neq v_2(n)$, I cannot find any solutions for this. I think that $G \in \{1,2\}$, but I cannot prove or disprove it. How can I find $G=\gcd(a^m+1,a^n+1)$ if $v_2(m) \neq v_2(n)$ ? Moreover, is there anything from my arguments that can be improved ? has anybody been successful getting pandas to work with QGIS's Python installation, on Windows? I've used the OSGeo4W installer to install QGIS2.2, which comes with Python 2.7 and Numpy 1.5.1. Any reasonably new version of pandas requires Numpy 1.6.1 or newer. So that seems like my main problem. I've tried: - Building an older version of pandas (e.g. 0.7.3 and 0.4.1) using easy_install, but that gives me a very long list of errors, at least the last of which are related to distutils\msvc9compiler.py - Using binaries of old pandas versions, but they are all built for Numpy 1.6.1 - Upgrading Numpy, which also gives me an error message. In case anybody is interested, the message ends with "File “C:\OSGeo4W\apps\Python27\lib\distutils\msvc9compiler.py”, line 299, in query_vcvarsall” newline “raise ValueERror(str(list(result.keys())))” newline “ValueError: [u’path’]"  I'm wondering if anybody else has ever been successful in getting pandas to work with a QGIS install on Windows??  It would be so easy if QGIS would ship with, say, a version of Numpy that's less than three years old. Does anybody know if such an upgrade is in the works for upcoming QGIS versions? Can I bind a (large) block of addresses to an interface? I know that the ip tool lets you bind multiple addresses to an interface (eg, ). Right now, though, I'm trying to build something on top of IPv6, and it would be really useful to have an entire block of addresses (say, a /64) available, so that programs could pick any address from the range and bind to that. Needless to say, attaching every IP from this range to an interface would take a while.  Does Linux support binding a whole block of addresses to an interface? In Ubuntu ISO MBR, why does a GPT partition overlap the boot partition, and make MBR uneditable? Adding shapefile or feature class as layer in ArcMap using ArcPy