How can I identify if a float within a string
How do I check if a string is a number (float)?
Why does changing a copy of an argument change the argument? It has been a long time since I have used calculus, and I am trying to understand how the mean and variance of the Laplace distribution with pdf $$f(x|\mu,\sigma) = \dfrac{1}{2 \sigma}\,e^{-\Large\frac{|x-\mu |}\sigma}$$ are derived.  I know that E$[X] = \mu$ and Var$[X] = 2\sigma^2$, but I don't understand how that happens.   Many thanks. I've seen this message several times whenever someone has a problem installing, upgrading or removing some piece of software, but I wonder, what does it mean, and more importantly, is possible to solve it?  (Reading database ... 81657 files and directories currently installed.)  Removing mongodb-10gen ...  arg: remove  invoke-rc.d: unknown initscript, /etc/init.d/mongodb not found.  dpkg: error processing mongodb-10gen (--remove):   subprocess installed pre-removal script returned error exit status 100  invoke-rc.d: unknown initscript, /etc/init.d/mongodb not found.  dpkg: error while cleaning up:   subprocess installed post-installation script returned error exit status 100  Errors were encountered while processing:   mongodb-10gen  E: Sub-process /usr/bin/dpkg returned an error code (1)   (the above is just an example, not my actual problem) Time taken for collision We have three particles at the vertices of equilateral triangle of side $d$. At $t=0$ they start moving in such away that at all instant of time each of them has a speed $v$ towards adjacent one. We have to find the time after which they will collide. I know that you can solve this by calculating from reference frame of any one particle, but I want a way to solve this by calculating the total distance traveled first in ground frame and then dividing by speed. How long will it take for Google's disavow tool to work? I had updated the disavow list on March 18th  with spammy domains which were linked to my site. Those links still show up in Google Search Console.  I Wanna know how long does it need to take effect? Where can I find out about Stack Overflow history? I'd like to know how Stack Overflow and other sites started - which was first, who initiated it (OK, that's on the link below) and why, how the different sites evolved, how the rules evolved, etc.  Where can I find such information?  Of course, I know I can look at  for a brief overview but I'm wondering if there is info on this site, particularly more detailed.. Looking for a short story about a boy discovering that the government puts mind control chemicals in his cereal I would have read this around 1985-1998 because I remember being in school at the time. It may have been in a short story collection with "The Ugly Little Boy" and a story about a family dealing with people in the future coming back to enhance the intelligence of their baby with enfante terrible results. A boy, grade school age or so and very intelligent, discovers (or possibly just decides) that there are drugs in the food that prevent one from thinking critically. The details are kind of fuzzy in my head, but I remember that he at one point distills the chemical from his cereal, which he'd detected as having a high concentration, and overdoses. He's convinced that the government is trying to silence him — a scene that sticks out in my mind was him falling on a moving sidewalk and tearing his clothing as he tries to escape two "men in black" type figures that are pursuing him. The short story ended with him deciding that he was better off just consuming the food and being happy in his ignorance.  Years later, as an adult learning about mental illness, it struck me that the story was slightly ambiguous as to whether there actually were chemicals, and that the use of drugs that dulled his creativity and intelligence, and the decision to take them anyhow, was reminiscent of the feelings that manic people have toward their medications.  Anyone know what this one was? What is this yellow and white mass inside my red cabbage? Bold row in table aligned with dcolumn English questions and negation with *do* in syntax Will the below code cause memory leak in c++ class someclass {};  class base {     int a;     int *pint;     someclass objsomeclass;     someclass* psomeclass; public:     base()     {         objsomeclass = someclass();         psomeclass = new someclass();         pint = new int();          throw "constructor failed";         a = 43;     } }  int main() {     base temp(); }   In the above code, the constructor throws. Which objects will be leaked, and how can the memory leaks be avoided?  int main() {     base *temp = new base(); }   How about in the above code? How can the memory leaks be avoided after the constructor throws? Modify TikZ coil decoration Can I modify the existing tikz coil decoration, so that the downstrokes are not drawn in a certain interval, to produce a picture like this?    Edit: Previous attempts, code and MWE has been moved to or superseded by my own answer. How do you rename root? Not that it's a very good idea to change it, but for fun. According to  post, there are still some problems even after changing entries in /etc/passwd, /etc/shadow, and /etc/sudoers. Any suggestions? Is there a number whose absolute value is negative? I mean a average human can run at his full speed for 15 to 20 mins before getting tired. Trained athletes can go on running for much more time without tiring out.  Do Superheroes like Quicksilver or Flash ever get tired due to excessive running? I noticed with the holiday patch that there are new trees and shrubs that spawn on my land.  One popped up today, being specifically an X-Mas tree - which costs 25,000 gold to remove.   Is there any benefit to removing this X-Mas tree?  Is there any benefit to leaving it there?    It is noticeably the most expensive obstacle to remove yet. dollar-terminated strings In my assembly language class, our first assignment was to write a program to print out a simple dollar-terminated string in DOS.  It looked something like this:  BITS 32     global _main  section .data     msg db "Hello, world!", 13, 10, ’$’  section .text _main: mov ah, 9 mov edx, msg int 21h ret   As I understand it, the $ sign serves to terminate the sting like null does in C.  But what do I do if I want to put a dollar sign in the string (like I want to print out "it costs $30")?  This seems like a simple question, but my professor didn't know the answer and I don't seem to find it using a google search. RSA encryption with private key and decryption with a public key How would you explain why $e^{i\pi}+1=0$ to a middle school student? Hi I was asked by a friends child who is in middle school why $e^{i\pi}+1=0$. Now I couldn't think of a way to explain it so he would understand. Albert Einstein once said “If you can't explain it simply, you don't understand it well enough” so how would I explain it. What else do I need to produce two dots above o?