operator-precedence | 易学教程

Why does i|= j|= k|= (j+= i) - - (k+++k) - - (i =+j) == 11?

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问题 I came across this code in a project I have started working on. The original developer is no longer available, and I can't make any sense of it: k = (j = (i = 0) + 2) + 1; return i|= j|= k|= (j+= i) - - (k+++k) - - (i =+j); It produces a value of 11 . How does this work? What is the =+ operator? What is the +++ operator? What is the - - operator? What is the |= operator? 回答1: What is the =+ operator? That's two operators, one assignment operator, = , and one unary plus, + , which does nothing

gcc linker library search order; paths plus static vs shared

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Reading through the gcc manual, I believe the following two statements are true: Library search paths specified on the command line are searched before "default" paths (which I assume means stuff in the LIBRARY_PATH environment variable) Shared libraries will be linked in preference to static libraries (in the absence of flags saying to do otherwise) But which of these two dominates? For example, if I type gcc myprog.cpp -o myprog -Lmypath -lmylibrary and in mypath there is the static library "libmylibrary.a", and in some place specified in LIBRARY_PATH there is a shared library "libmylibrary

C operator precedence, logical vs unary in a++ && b++ || ++c

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问题 In the follwing code, int a = 1, b = 2, c = 3, d; d = a++ && b++ || c++; printf("%d\n", c); The output will be 3 and I get that or evaluates first condition, sees it as 1 and then doesn't care about the other condition but in c, unary operators have a higher precedence than logical operators and like in maths 2 * 3 + 3 * 4 we would evaluate the above expression by first evaluating product and then the summation, why doesn't c do the same? First evaluate all the unary operators, and then the

Operator precedence in Python -PEMDAS

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问题 I read about python following PEMDAS that is precedence of multiply is more than division. I ran the following script print 6*2/1*2 Thus python should interpret this like 12/2 i.e 6 , since precedence of multiplication is more than division. But, the answer is 24. Could anyone let me know where the problem is? Thanks! 回答1: * has the same operator precedence as / . Operators in the same group evaluate left to right, so your expression evaluates as: 6*2 = 12 / 1 = 12 * 2 = 24 回答2: Order of

CSS: Child selector higher precedence than class selecctor?

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I have the following HTML: <div class="form-square"> <div class="seven-col"> Hello World! </div> </div> And the following CSS: div.form-square > div { padding: 50px; } .seven-col { padding: 0; } Firefox and Firebug is using the first of the two CSS rules. How come "div.form-square > div" has higher precedence than ".seven-col" which is more specific? div.form-square > div consists of 1 class selector + 2 type selectors (plus a child combinator). .seven-col consists of 1 class selector. The number of class selectors is equal, so the comparison is done in type selectors. The first selector has

Priority of AND and OR operator in Mysql select query [closed]

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I have a written a mysql select query to fetch schedule details based on origin states,origin city,destination state and destination city. In my query i have used AND and OR operator. Here is my query, SELECT * FROM TruckLoadSchedule ts WHERE ts.originState IN (states) AND ts.originCity IN (cities) OR ts.destState IN (states) AND ts.destCity IN (cities); But I need to know the priority of AND and OR operator in the above query, i mean to say will it do something like this (X AND Y) OR (M AND Q) internally? Yes, AND has higher precedence than OR. x and y are bound together, m and q are bound

Why does “**” bind more tightly than negation?

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I was just bitten by the following scenario: >>> -1 ** 2 -1 Now, digging through the Python docs, it's clear that this is intended behavior , but why? I don't work with any other languages with power as a builtin operator, but not having unary negation bind as tightly as possible seems dangerously counter-intuitive to me. Is there a reason it was done this way? Do other languages with power operators behave similarly? That behaviour is the same as in math formulas, so I am not sure what the problem is, or why it is counter-intuitive. Can you explain where have you seen something different? "**

“C - C++” joke about postfix/prefix operation ordering

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问题 My friend sent me a joke: Q. What's the difference between C and C++? A. Nothing, because: (C - C++ == 0) I tried to change order and got stuck. Look at this code: public class Test { public static void main(String args[]) { int c = 10; System.out.println(c++ - c); System.out.println(++c - c); } } Why does it return: -1 0 I understand postfix and prefix increment. Why isn't this the result? 0 1 回答1: Because in the first example, c starts out 10. c++ increments c and returns 10, so the second

Is python assignment strictly evaluated right to left? [duplicate]

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This question already has an answer here: Is the right-hand side of an assignment always evaluated before the assignment? 2 answers In other words is d = {} d["key"] = len(d) safe in Python? I know this is undefined behaviour in C++ ; where the program might get a reference to the element before computing the value it's going to assign to it. Is this similar in Python or is len(d) always computed before d.__getitem__("key") ? Abhijit Yes, in Python it is safe: the evaluation order of an expression is from left to right, but in an assignment statement the right side is evaluated before the

int[] arr={0}; int value = arr[arr[0]++]; Value = 1?

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问题 Today I came a cross an article by Eric Lippert where he was trying to clear the myth between the operators precedence and the order of evaluation. At the end there were two code snippets that got me confused, here is the first snippet: int[] arr = {0}; int value = arr[arr[0]++]; Now when I think about the value of the variable value, I simply calculate it to be one. Here's how I thought it's working. First declare arr as an array of int with one item inside of it; this item's value is 0.