C Programming: How to read the whole file contents into a buffer
How to read the content of a file to a string in C?
Showing that a function is not differentiable It seems that I'm missing something about this.  First of all, the series is convergent: $\lim_{n\rightarrow\infty}\frac{2^{-n-1} (n+1)^2}{2^{-n} n^2}=\frac{1}{2}$ (ratio test)  What I tried to do is to find a limit of a partial sum $\lim_{n\rightarrow\infty}S_n$ as follows: $S_n=\frac{\frac{1}{6} n (n+1) (2 n+1)}{\frac{1-\left(\frac{1}{2}\right)^n}{2 \left(1-\frac{1}{2}\right)}}$. Still, the limit is $\infty$ and I'm clearly doing something wrong. Compact subset in colimit of spaces There is a button in the "basic math assistant" which wraps highlighted text in chosen brackets. Is there no keyboard command for this? Altium: How can I edit a component from a library LaTeX macro expander Remove all attributes from html tags PBKDF vs HKDF for pretty long key I'm developing a messenger application with encrypted chats.   In the first version of the app I've used PBKDF2 (10000 iterations, SHA1, random salt) to extend a short user password and generate keys to encrypt (AES256) and sign message (HMAC).  In the current version of the app I generate a random 130-bit key and use it instead of a user password. I think that using PBKDF2 with such a key has some overhead.   I see 2 possible ways to improve the current approach:   Keep using PBKDF2 and decrease iterations to 1 or 10. Don't use PBKDF2 and use HKDF instead.   What are the advantages and disadvantages of each approach? Are there any other options? Merge two PDF files containing even and odd pages of a book I have two searchable PDF  documents, say even.pdf and odd.pdf which contain even and odd pages of a book, respectively.   I can decompile each PDF to separate files 001.pdf 002.pdf 003.pdf, et cetera. The question is how to merge them?  They are both even and odd sequences numbered 1, 2, 3. If the numbering in the decompile process with pdftk were different, e.g. 1, 3, 5 for even and 2, 4, 6 for odd instead of 1, 2, 3, 4, I could simply merge them.  Can I do this any other way? Is your mount an enemy of your target in terms of triggering sneak attack? I was working on building a Zorro character and this question came up: if a rogue is riding on a mount, is that mount considered an ally, or, specifically, an "enemy" of your target?  One of the ways Sneak attack can be trigged is...     "... if another enemy of the target is within 5 feet of it, that enemy   isn’t incapacitated, and you don’t have disadvantage on the attack   roll."   My assumption is yes. Every mount I'm aware of has some kind of attack at its disposal, and thus they represent a threat to your target in addition to the increased threat potential they grant you as the rider. Moreover, if a gnome can proc a sneak attack by acting as a distraction, I don't know why a warhorse wouldn't be able to. That said, is there anything in the books or elsewhere that defines what "enemy of the target" is allowed to include? I'd like to install both Ubuntu 12.04 and Windows XP on a Dell laptop, and I was thinking about using a dual boot structure, and using the bulk of my hard drive as empty hard drive space to share files between the two operating systems (so choice of file system type is very important in this set-up).     The kind of partitioning structure I would like to use is  Partition 1 - Ubuntu 12.04 (root) (20GB)  Partition 2 - Ubuntu /home        (20GB)  Partition 3 : Free Space          (560GB)  Partition 4 : Windows XP          (35GB)  Partition 5 : SWAP                (3GB)  (Total Hardrive Capacity is ~640GB)    My question is; what is the best way to go about setting up this kind this system?   Should I install Windows XP first and setup the partitions, and then install Ubuntu which I believe will install the GRUB bootloader for OS booting choice   or   Do I install Ubuntu first, setting up the available partitions and then perform a WIndows install?  Please let me know if there is anything in this setup that I have left out and should know about, including things related to setting particular partitions as logical or primary, and whether the boot partition and the filesystem partition should actually be two separate partitions. I have a Git repo that I have deleted four files from using rm (not git rm), and my Git status looks like this:  #    deleted:    file1.txt #    deleted:    file2.txt #    deleted:    file3.txt #    deleted:    file4.txt   How do I remove these files from Git without having to manually go through and add each file like this:  git rm file1 file2 file3 file4   Ideally, I'm looking for something that works in the same way that git add . does, if that's possible. How to integrate Tikz code in SW? I'd like to know how to insert Tikz code in Scientific Workplace tex file. Since SW doesn't support Tikz directly, now I just create Tikz code in another tex editor and export as pdf. Then I convert pdf to images, and import images into SW. When do "per day" spell-like abilities recover in 3rd edition? Verification that $\lim_{x \to a}\frac{f(x)-f(a)}{x-a}$ and $\lim_{h\to 0}\frac{f(a+h) -f(a)}{h}$ are equivalent definitions of the derivative. I wanted to verify that for definition of the derivative it is true that:  $$ \lim_{x \to a}\frac{f(x)-f(a)}{x-a}= \lim_{h\to 0}\frac{f(a+h) -f(a)}{h}$$  If I denote $h=x-a$,  we can  let $x\to a$, this means that $h \to 0$. Also notice that $f(x)=f(a+h)$ $$ \lim_{x \to a}\frac{f(x)-f(a)}{x-a}=\lim_{h \to 0}\frac{f(a+h)-f(a)}{h}$$ As desired. Is the main idea here really just to use a variable substitution? I suppose there is some formal theorem I also use here that when $f(x) \to y$  we can let $g(f(x)) \to g(y)$ if the function $g$ is continuous. How to solve this limit: $\lim\limits_{x\to0}\frac{(1+x)^{1/x}-e}x$? I tried to evaluate $$\lim_{x\to0}\frac{(1+x)^{1/x}-e}x$$but all my efforts were in vain . L'Hospital rule becomes very complicated. How can I rotate an object based on another's offset to it? I have a 3D model of a turret that con rotate around the Y-axis. This turret has a cannon that is significantly off the center of the object. I want the cannon, not the turret, to aim at a specified target. I can only rotate the turret, however, and thus I don't know what equation I need to apply in order to accomplish by objective.  The following image illustrates my problem:  If I have the turret "LookAt()" the target, a laser originating from the cannon will completely miss said target.   If this were a completely top-down scenario, and the cannon were exactly parallel to the turret, then my logic tells me that the fake target should be located at a position that's equal to the actual target plus an offset that's equal to that between the turret and the cannon. However, in my actual scenario, my camera is angled 60º, and the cannon has a slight rotation.  The following image illustrates the scenario:   I'm not sure exactly why, but if I apply that same offset, it only seems to work while aiming at certain distances from the turret.  Is my logic flawed? Am I missing something fundamental here?  Final Edit: the solution provided by @JohnHamilton latest update solves this problem with perfect precision. I have now removed the code and images that I used to illustrate my incorrect implementations. I am developing a game with a Minecraft-like terrain made out of blocks. Since basic rendering and chunk loading is done now, I want to implement block selecting.  Therefore I need to find out what block the first person camera is facing. I already heard of unprojecting the whole scene but I decided against that because it sounds hacky and isn't accurate. Maybe I could somehow cast a ray in view direction but I do not know how to check the collision with a block in my voxel data. Of course this calculations must be done on the CPU since I need the results to perform game logic operations.  So how could I find out which block is in front of the camera? If it is preferable, how could I cast a ray and check collisions? Using a transistor as a switch I am attaching a motor to an ATmega32 chip. I want to build an H-bridge but before doing that, I want to control the motor using the chip. I bought few NPN Transistors from RadioShack. I have 5V running though the breadboard. I attached Vcc to the Collector, Base to the Pin, and Emitter to the motor. And other wire of motor is hooked up to Ground. Unfortunately, the power coming out of the transistor is too low, the motor is barely moving (As opposed to when I hook up my motor straight to 5V). What is wrong? Do I need a different transistor or is my setup wrong? If it is the transistor, can you please recommend the right one, I am not too good at those. Why are place names in some old books a capital letter followed by dashes, and what is this phenomenon called? This is something very odd I have noticed in some older books, most recently in "Crime and Punishment" by Dostoyevsky.  Place names, when not specifically essential or well-known, are made up of one letter followed by a line of underscores (i.e. "X_____").  I think I recall reading something similar in another older work, possibly by Jane Austin?  Apologies if this is a duplicate; I've searched quite extensively and can't seem to figure it out.  I don't know a name for this, so can't search easily for it.