I am trying count total number of files in all the sub folder of a given path. I am using recursive function call. What could be the reason?  Code:  int iCount =0;  getFileCount(_dirPath, out iCount);  private void getFileCount(string _path, out int iCount ) {               try     {         // gives error :Use of unassigned out parameter 'iCount' RED Underline         iCount += Directory.GetFiles(_path).Length;          foreach (string _dirPath in Directory.GetDirectories(_path))             getFileCount(_dirPath, out iCount);     }     catch { } }
What is the difference between ref and out parameters in .NET? What are the situations where one can be more useful than the other? What would be a code snippet where one can be used and another can't?
Intersection of three vector subspaces We say that two vector subspaces $U,W\subset V$ intersect transversally (written $U\pitchfork W$) if $U+W=V$.  Let $V_1,V_2,V_3$ be vector subspaces of $V$ where $\dim V=n$. We say they intersect normally if $V_i\pitchfork(V_k\cap V_l)$  for $i\ne k,l$. Prove that $V_1,V_2,V_3$ intersect normally if  the following condition holds:  $\operatorname{codim}(V_1\cap V_2\cap V_3)=\operatorname{codim} V_1+\operatorname{codim} V_2+\operatorname{codim} V_3,$   where $\operatorname{codim} V_i=n-\dim V_i$.  How to approach this problem? I tried to order dimensions of $V_i$ but I got that the LHS is $\ge n-\min (\dim V_i,i=1,2,3)$ and the RHS is $\le 3( n-\min (\dim V_i,i=1,2,3))$ which does not lead anywhere. What is the right way to do this? Can I use my single entry Schengen visa to go to a different Schengen country than originally planned? My friends and I planned to visit Germany, so I got a single entry tourist Schengen visa to Germany. However, my travel plans have changed since then, because my friends are going to Italy instead. I don't have time to apply for a visa to Italy, but I have been told that I can use my Schengen visa to enter Italy. Is that true? Is the Discrete Topology on $X$ the Only One Containing All Infinite Subsets of $X$? Prove or find counterexamples.  Let $X$ be an infinite set and $T$ be a topology on $X$. If $T$ contains every infinite subset of $X$, then $T$ is the discrete topology. Show that if $x$, $y$, $z$ are integers such that $x^2 + y^2 = z^2$, then at least one of them is divisible by $2$, at least one is divisible by $3$, and at least one is divisible by $5$.  I know that $x,y,z$ are sides of a right-angled triangles. If I start putting values, then I can show, but have no clue about mathematical approach.  How do I solve it mathematically, using modular arithmetic? Please make the multiple comment timer less annoying (non-resetting etc.) As a little feature to prevent comment spam, you can only enter one comment every 15 seconds. That's a very reasonable limitation, since you very rarely have a good reason to write comments that quickly. I've only seen it twice at all, I think, but both times it was extremely annoying.     Only 1 comment allowed per 15 seconds; timer reset.   The reason is that every time you hit the limit, the 15 seconds begin anew. You have no indicator that tells you when you are allowed to comment again, and if you hit enter after just 14 seconds, you're back to zero. Yesterday, I went through four cycles of not quite 15 seconds, counting in my head, before I got a myself a coffee and tried again afterwards.  I suggest that you do one or more of the following (in decreasing order):   Make the counter non-restarting Add a visible countdown Make it clearly visible that you can't comment right now You can actually increase the waiting time, if it is clearly visible and there is no unnerving invisible countdown. Actually, just remove all comment fields after one comment, and tell the user to reload the page. Just please don't have UI elements that look like they would work, but feel like they are trolling you. I solved the Lagrangian of a simple pendulum (with help from online examples as this concept is new to me) and ended with the following: $$\ddot{\theta}+\omega^2\theta=0$$ But in the example I was following, the next line written was this: $$\theta(t) = A\cdot\sin(\omega t + \Phi)$$ And I don't know what steps they took to get there? Why would one limit username format? Many websites when ask you to create a new "username", will limit you in some way, most often like "username should only contain letters and underscores" or something alike.  This results in inability to use my email as username and forces me to come up with new unique string all the time.  What is the rationale behind this?  Why not just let users use their emails, as a simple to remember and always unique?   What is generally wrong with having symbols like *&amp;%$#@ as a part of username? package makeidx: print first letter for each group of keys I've created index with makeidx package. It works. What really need is to print the first letter above every group of keys (i.e. referring to the image I want to print the red letter, that I have manually inserted). How to reinstall yum? How do they film continuous blood pooling? I'm level 16 which makes battling many Draugr Wrights hard. My defense is just way too low, and I don't have enough time or strong enough magic to take them out.   My one-handed skill is at 62 and my strongest weapon does 33+10 enchanted damage. Are there any ways to level up easily? First time player in a group figuring out things as we all go.  I just hit level four as a Ranger, and I get to improve one ability score of my choice by 2, or I can increase two ability scores of my choice by 1.  My first thought was Strength, as I've been rocking a score of 11 with a mod of +0 so far. But I read that Rangers use (wisdom mod + 10) for their spell casting modifier. Currently my wisdom is 13, with a mod of +1. If I increase either STR or WIS, will the modifier increase as well? How and why?  A Monk in our party went from 9 CON to 11 during their ability score improvement, and by doing so their modifier went from −1 to 0.  We're all pretty new, so between eight people we're currently sharing one book, and all trying to locate our own copies for later campaigns. That's making it… inefficient for us to learn these things quickly. I am trying to setup a trace flag to debug. When I select User in the dropdown and try to find System in there. It doesn't show up. What can I do ? How to calculate overlap between empirical probability densities? I'm looking for a method to calculate the area of overlap between two kernel density estimates in R, as a measure of similarity between two samples. To clarify, in the following example, I would need to quantify the area of the purplish overlapping region:  library(ggplot2) set.seed(1234) d &lt;- data.frame(variable=c(rep("a", 50), rep("b", 30)), value=c(rnorm(50), runif(30, 0, 3))) ggplot(d, aes(value, fill=variable)) + geom_density(alpha=.4, color=NA)     A similar question was discussed , the difference being that I need to do this for arbitrary empirical data rather than predefined normal distributions. The overlap package addresses this question, but apparently only for timestamp data, which doesn't work for me. The Bray-Curtis index (as implemented in vegan package's vegdist(method="bray") function) also seems relevant but again for somewhat different data.  I'm interested in both the theoretical approach and the R functions I might employ to implement it. JTable won't show column headers Wilson and Fermat's Theorem How should I phrase a question that must be answered with an ordinal number (e.g., the third prime)? I want to make a question having an answer as follows:     5 is the third prime number.   The bold part is the answer. How to phrase the question? How to prevent updating of a specific package? Because of  I'd like to prevent apt-get upgrade and Update Manager from updating the "libgtk2.0-0" package.   How can this be achieved? Let $A [a_{i,j}]$  and $B =[b_{ij}]$   be two diagonal matrices in   $M_n(F)$. Let $i \ne j \in \left\{1, \ldots, n \right\}$. Using the   product rule, we obtain      $$(AB)_{ij} = \sum_{k=1}^{n} a_{ik}b_{kj}$$      We claim that $a_{ik}b_{kj} =0$ for all $k \in \left\{1, \ldots, n \right\}$ thus $(AB)_{ij}=0$ for all $i \ne j$ and $AB$ is diagonal. To    prove the claim, note that since $i \ne j$ , we have $i \ne k$ or $    k\ne j$. Thus either $a_{ik} = 0$ (since $A$ is diagonal) or $b_{kj} =  0$ (since $B$ is diagonal), thus in all cases $a_{ik}b_{kj}=0$ and the   claim is proved.   Where does the bit "we have $i \ne k$ or $k\ne j$" come from? I understand that since $i \ne j$, and $k$ and $j$ run over the same set of natural numbers, we also have $i \ne k$. But the "or $k \ne j$" baffles me. I understand that $k \ne j$ implies that we can have $i=k$. But that's from the other direction ($\Longleftarrow).$  Also, when it says $a_{ik}=0$ or $b_{kj}=0$ it's talking about when $i \ne k$ or $k \ne j$ right? Many thanks. I've been perusing the internet looking for interesting problems to solve. I found the following problem and have been going at it for the past 30 minutes with no success:     Find a function $f: \mathbb{R} \to \mathbb{R}$ satisfying $f(f(x)) = -x$ for all $x \in \mathbb{R}$.   I am also wondering, can we find $f$ so that is continuous?  I was thinking of letting $f$ be a periodic function, and adding half the period to x each time. I had no success with this, and am now thinking that such a function does not exist.  Source: