operator-precedence

问题 Please have a look at the following code: int i=5; boolean b = i<5 && ++i<5;//line 2 System.out.println(i);//line 3, prints 5 In line 2, according to my understanding: Since among all the operators, ++ has highest precedence ++i should be evaluated first. But line 3 actually is printing i=5 (and not 6 ). Meaning, && has evaluated before ++ operator. How is it possible? EDIT: From the answers I see that "In Java, all expressions are evaluated from left to right.". But when does actually

问题 This question already has answers here : Why does the expression 0 < 0 == 0 return False in Python? (9 answers) Closed 4 years ago . How is it that, in Python 2.7, the following True == 'w' in 'what!?' behaves differently than both (True == 'w') in 'what!?' and True == ('w' in 'what!?') ? >>> True == 'w' in 'what!?' False >>> (True == 'w') in 'what!?' Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'in <string>' requires string as left operand, not bool >>>

问题 $a = 1; $a OR $a = 'somthing' echo $a; //1 Why? If = have much precedence then 'OR' then why OR execute first? 回答1: Because if OR has higher precedence then $a OR $a = 'somthing' will be parsed as: ($a OR $a) = 'somthing' that would be technically wrong because you can't assign to an expression (while programmers would like to write expression like this is coding so it should be a valid expression). because precedence of or operator was low hence the expression $a OR $a = 'somthing' pareses

问题 I have a trouble with next case: template<typename T> void test(const T &ref){ cout << "By reference"; } template<typename T> void test(const T *ptr){ cout << "By pointer"; } Any parameter that I sent to the test() method will always pass to overloading with reference. Even this: int *p = 0; test(p); Can someone tell me why reference has so high priority and the place in standart where to read about this. Oh... I was inattentive! I have to specify both const and non-const overloading for a

问题 I cannot produce example in Python which shows Boolean operator precedence rules combined with short circuit evaluation. I can show operator precedence using: print(1 or 0 and 0) # Returns 1 because `or` is evaluated 2nd. But the issue with short circuiting shows up when I change it to this: def yay(): print('yay'); return True def nay(): print('nay') def nope(): print('nope') print(yay() or nay() and nope()) # Prints "yay\nTrue" For each of 4 possibilities when expression before or is True

问题 hindent changed my code to: do download i inputFile onException (callProcess (List.head args) (List.tail args)) (removeFileIfExists name) `finally` removeFileIfExists inputFile I can't determine if the finally applies to the rest of the do block, or just the state beginning onException . According to this, If you see something unexpected in a list, like where, insert a closing brace before instead of a semicolon. I'm unsure if that rule is applying here. Does the `finally` apply to the rest

问题 The C++17 standard revised the definitions of the order of operations for the C++ language by a rule stating, to the effect: In every simple assignment expression E1=E2 and every compound assignment expression E1@=E2, every value computation and side-effect of E2 is sequenced before every value computation and side effect of E1 However, when compiling the following code in GCC 8.1 with -std=c++17 and -Wall int v[] { 0,1,2,3,4,5,6,7 }; int *p0 = &v[0]; *p0++ = *p0 + 1; cout << "v[0]: " << v[0]

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Is the comma in a variable list a sequence point? If I have the following code does the comma act as a normal sequence point, or is the behaviour undefined? int i = 1, j = i; I don't actually plan to use this (our internal standard prohibits even int i, j ) but I was curious and it prooved oddly tricky to google. 回答1: It's well-defined: 8. Declarators: [dcl.decl] 3) Each init-declarator in a declaration is

问题 I am creating a formal spec for a very simple rule language, very simple. I want to use EBNF as this is a standard but I can't figure out how to specify order of operations. Here is the specification so far. rule = statement, { (‘AND’|’OR’), statement}; variable = ‘$’,alphabetic character, {alphabetic character | digit}; statement = variable, [ ‘count’,[white space ],’>’,[white space],number ]; alphabetic character = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J" | "K" | "L" | "M"

问题 I was looking at this page: https://en.cppreference.com/w/c/language/operator_precedence What caught my attention was that the only description of the parenthesis operator was function call . Does this mean that the expression x = a * (b+c)-(d*e) has two function calls? I searched in C grammar and C standard but I was unable to find anything that either supports or contradicts this. 回答1: Parenthesis can be used as a function call operator, but that's not the only thing they're used for. They