operator-precedence

问题 This question already has answers here : Is short-circuiting logical operators mandated? And evaluation order? (7 answers) How does C++ handle &&? (Short-circuit evaluation) [duplicate] (7 answers) Closed 6 years ago . Given two conditions with an && connection. I know that the order of evaluation is from left to right. But if the first condition resolves to false, it the second condition guaranteed to not get evaluated? #define SIZE bool array[SIZE]; int index; // play with variables // ...

问题 This question already has answers here : Is short-circuiting logical operators mandated? And evaluation order? (7 answers) How does C++ handle &&? (Short-circuit evaluation) [duplicate] (7 answers) Closed 6 years ago . Given two conditions with an && connection. I know that the order of evaluation is from left to right. But if the first condition resolves to false, it the second condition guaranteed to not get evaluated? #define SIZE bool array[SIZE]; int index; // play with variables // ...

问题 This question already has answers here : Is short-circuiting logical operators mandated? And evaluation order? (7 answers) How does C++ handle &&? (Short-circuit evaluation) [duplicate] (7 answers) Closed 6 years ago . Given two conditions with an && connection. I know that the order of evaluation is from left to right. But if the first condition resolves to false, it the second condition guaranteed to not get evaluated? #define SIZE bool array[SIZE]; int index; // play with variables // ...

问题 I know the basic rule regarding the multiple assignment in Python: all expressions at the right part of the assignment are evaluated first then evaluated values are bound to variables at the left part But actually I encountered something quite different and a little more complicated; I would like to know if I may rely on it. While debugging an algorithm, I suddenly discovered that a bug was related to the line: k[s], k[p] = k[p], None Because my algorithm found a case where s and p were equal

问题 I have an interface IRenderable and a class that manages rendering all instances of classes implementing the interface. I have many classes in my code and will expect others to create classes that implement the same interface. Due to the nature of rendering I want to say things like "Draw instances of this class before instances of this class". The typical approach is to have every class implement a DrawOrder property, however I dislike this because classes don't have a definite draw order

问题 I always use brackets in sql queries. But I have example: DELETE FROM prog WHERE prog_start >= $1 AND prog_start < $2 OR prog_end > $1 AND prog_end <= $2 Is it equal to : DELETE FROM prog WHERE ( prog_start >= $1 AND prog_start < $2 ) OR ( prog_end > $1 AND prog_end <= $2 ) or not ? 回答1: In SQL the AND operator takes "precedence" over OR operator. PostgreSQL adheres to the spec here. You can the exact precedence in PostgreSQL in the docs Lexical Structure: Operator Precedence. So in your case

问题 This question already has answers here : Something we found when using comma in condition ternary operator? [duplicate] (4 answers) What's the precedence of comma operator inside conditional operator in C++? (3 answers) Closed 6 years ago . I have no idea why the result of the two sub programs below are different: int a , b; a = 13, b=12; (a > b)? (a++,b--):(a--,b++); // Now a is 14 and b is 11 a = 13, b=12; (a > b)? a++,b-- : a--,b++; // Now a is 14 but b is 12 However for these cases, the

问题 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? 回答1: div.form-square > div consists of 1 class selector + 2 type selectors (plus a child combinator). .seven-col consists of 1 class selector.

问题 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? 回答1: div.form-square > div consists of 1 class selector + 2 type selectors (plus a child combinator). .seven-col consists of 1 class selector.

问题 The documentation of seq function says the following: A note on evaluation order: the expression seq a b does not guarantee that a will be evaluated before b . The only guarantee given by seq is that the both a and b will be evaluated before seq returns a value. In particular, this means that b may be evaluated before a . If you need to guarantee a specific order of evaluation, you must use the function pseq from the "parallel" package. So I have a lazy version of sum function with