increment

Increment a database field by 1

由 风流意气都作罢 提交于 2019-11-26 15:02:38
With MySQL, if I have a field, of say logins, how would I go about updating that field by 1 within a sql command? I'm trying to create an INSERT query, that creates firstName, lastName and logins. However if the combination of firstName and lastName already exists, increment the logins by 1. so the table might look like this.. firstName----|----lastName----|----logins John Jones 1 Steve Smith 3 I'm after a command that when run, would either insert a new person (i.e. Tom Rogers) or increment logins if John Jones was the name used.. Sampson Updating an entry: A simple increment should do the

Pre-incrementation vs. post-incrementation

由 一世执手 提交于 2019-11-26 14:34:15
问题 How are they different? Here's what I'm thinking, but I'm not sure.... If you use pre-incrementation, for example in a for loop with ++j, then you are basically saying: "Make a copy of the value of j for use in the loop, then increment j, then go through the statements in the loop with the copy of j." If you are using post-incrementation in the same loop j++, then you are basically saying: "Make a copy of the value of j for use in the loop, then go through the statements in the loop with the

Java increment and assignment operator

由 只谈情不闲聊 提交于 2019-11-26 14:17:49
问题 I am confused about the post ++ and pre ++ operator , for example in the following code int x = 10; x = x++; sysout(x); will print 10 ? It prints 10,but I expected it should print 11 but when I do x = ++x; instead of x = x++; it will print eleven as I expected , so why does x = x++; doesn't change the the value of x ? 回答1: No, the printout of 10 is correct. The key to understanding the reason behind the result is the difference between pre-increment ++x and post-increment x++ compound

bool operator ++ and --

由 坚强是说给别人听的谎言 提交于 2019-11-26 12:06:47
问题 Today while writing some Visual C++ code I have come across something which has surprised me. It seems C++ supports ++ (increment) for bool, but not -- (decrement). It this just a random decision, or there is some reason behind this? This compiles: static HMODULE hMod = NULL; static bool once = false; if (!once++) hMod = LoadLibrary(\"xxx\"); This does not: static HMODULE hMod = NULL; static bool once = true; if (once--) hMod = LoadLibrary(\"xxx\"); 回答1: It comes from the history of using

Incrementing: x++ vs x += 1

由 喜你入骨 提交于 2019-11-26 11:37:37
问题 I\'ve read that many developers use x += 1 instead of x++ for clarity. I understand that x++ can be ambiguous for new developers and that x += 1 is always more clear, but is there any difference in efficiency between the two? Example using for loop: for(x = 0; x < 1000; x += 1) vs for(x = 0; x < 1000; x++) I understand that it\'s usually not that big of a deal, but if I\'m repeatedly calling a function that does this sort of loop, it could add up in the long run. Another example: while(x <

Prefix/Postfix increment operators

由 家住魔仙堡 提交于 2019-11-26 10:55:41
问题 I\'m wanting to make sure I understand pass-by-value vs pass-by-reference properly. In particular, I\'m looking at the prefix/postfix versions of the increment ++ operator for an object. Let\'s suppose we have the following class X : class X{ private: int i; public: X(){i=0;} X& operator ++ (){ ++i; return *this; } //prefix increment X operator ++ (int unused){ //postfix increment X ret(*this); i++; return ret; } operator int(){ return i; } //int cast }; First of all, have I implemented the

The difference between ++Var and Var++ [duplicate]

由 天涯浪子 提交于 2019-11-26 10:27:34
问题 This question already has an answer here: How do the post increment (i++) and pre increment (++i) operators work in Java? 14 answers In programming, particularly in Java, what is the difference between: int var = 0; var++; and int var = 0; ++var; What repercussions would this have on a for loop? e.g. for (int i = 0; i < 10; i++) {} for (int i = 0; i < 10; ++i) {} 回答1: tldr; Although both var++ and ++var increment the variable they are applied to, the result returned by var++ is the value of

How to Copy (and increment) Multiple Instances of a File Using Batch File

由 徘徊边缘 提交于 2019-11-26 10:03:49
问题 I need to create a batch file that copies a file and increments it upon placing it at the destination. Example. copy C:\\TEMP\\MyDoc.txt E:\\MyData\\ Essentially, I need this copy command to copy every time I start it (which it does now just fine). I would like it to increment the file name instead of overwrite it though. If I ran this three times or 100 times (never a certain number) I would like to see on the \"MyData\" folder: MyDoc.txt MyDoc(1).txt ... Or Copy (1) I\'m not really sure

R: += (plus equals) and ++ (plus plus) equivalent from c++/c#/java, etc.?

由 旧城冷巷雨未停 提交于 2019-11-26 09:29:02
问题 Does R have a concept of += (plus equals) or ++ (plus plus) as c++/c#/others do? 回答1: No, it doesn't, see: R Language Definition: Operators 回答2: Following @GregaKešpret you can make an infix operator: `%+=%` = function(e1,e2) eval.parent(substitute(e1 <- e1 + e2)) x = 1 x %+=% 2 ; x 回答3: R doesn't have a concept of increment operator (as for example ++ in C). However, it is not difficult to implement one yourself, for example: inc <- function(x) { eval.parent(substitute(x <- x + 1)) } In that

Why does this go into an infinite loop?

由 心不动则不痛 提交于 2019-11-26 09:14:16
I have the following code: public class Tests { public static void main(String[] args) throws Exception { int x = 0; while(x<3) { x = x++; System.out.println(x); } } } We know he should have writen just x++ or x=x+1 , but on x = x++ it should first attribute x to itself, and later increment it. Why does x continue with 0 as value? --update Here's the bytecode: public class Tests extends java.lang.Object{ public Tests(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return public static void main(java.lang.String[]) throws java.lang.Exception; Code: 0: iconst_0
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