logical-operators

问题 Languages like i.e. Java and C# have both bitwise and logical operators. Logical operators make only sense with boolean operands, bitwise operators work with integer types as well. Since C had no boolean type and treats all non-zero integers as true, the existence of both logical and bitwise operators makes sense there. However, languages like Java or C# have a boolean type so the compiler could automatically use the right kind of operators, depending on the type context. So, is there some

问题 I'm trying to use the logical_and of two or more numpy arrays. I know numpy has the function logical_and() , but I find the simple operator & returns the same results and are potentially easier to use. For example, consider three numpy arrays a, b, and c. Is np.logical_and(a, np.logical_and(b,c)) equivalent to a & b & c ? If they are (more or less) equivalent, what's the advantage of using logical_and() ? 回答1: @user1121588 answered most of this in a comment, but to answer fully... "Bitwise

问题 I'm trying to use a conditional expression in an el expression used in jsf, but it does not work. <h:outputText value="#{(sel.description !=null) && (sel.description !='') ? sel.description : 'Empty description'} - "/> but it does not work, the compiler says: Error Traced[line: 118] The entity name must immediately follow the '&' in the entity reference. Do you have any suggestions? Thank you! 回答1: You seem to be using Facelets (which is perfectly fine). It's however a XML based view

问题 As a php neewbie , I try to read a lot of other people´s code in order to learn. Today I came across a line like this : if ( stripos($post_to_check->post_content, '[' . $shortcode) !== false ) I was wondering what is the difference between !==false and ==true If someone can explain that to me, It would be greatly appreciated. ..and if there is no real difference - what would be the reasons to use the quoted one over the other ?? 回答1: PHP is a loosely typed language. == match the both values

问题 When I try this: $a = 1; $b = 2; print ($a && $b) . "\n"; The result is 2. Why? 回答1: Quote perlop: The "||", "//" and "&&" operators return the last value evaluated (unlike C's "||" and "&&", which return 0 or 1). The resulting 2 is considered true by Perl, so that when you use the && operator in a logical condition, everything works as expected. The added bonus is that you can use the logical operators in other contexts as well: sub say_something { say shift || 'default'; } say_something(

问题 Bitwise operators work on bits, logical operators evaluate boolean expressions. As long as expressions return bool , why don't we use bitwise operators instead of logical? In this example I use bitwise instead of logical: #include <iostream> int main(){ int age; std::cin >> age; if( (age < 0) | (age > 100) ) // eg: -50: 1 | 0 = 1 std::cout << "Invalid age!" << std::endl; // if( (age < 0) || (age > 100) ) // std::cout << "Invalid age!" << std::endl; return 0; } 回答1: One possible answer is:

问题 This question already has answers here : Logical operators in JavaScript — how do you use them? (2 answers) Closed 4 years ago . When I type in browser's console: console.log(2 && 3) it results always with second number (in this case 3): 3 Can someone explain me why? 回答1: If the left hand side of && evaluates as a false value, the whole expression evaluates as the left hand side. Otherwise it evaluates as the right hand side. 2 is a true value, so 2 && 3 is 3 . For comparison, try console.log

问题 Is there a better way to write the following conditional in javascript? if ( value == 1 || value == 16 || value == -500 || value == 42.42 || value == 'something' ) { // blah blah blah } I hate having all of those logical ORs strung together. I'm wondering if there is some kind of shorthand. Thanks! 回答1: var a = [1, 16, -500, 42.42, 'something']; var value = 42; if (a.indexOf(value) > -1){ // blah blah blah } Upd: Utility function sample as proposed in comments: Object.prototype.in = function(

问题 Is there a better way to write the following conditional in javascript? if ( value == 1 || value == 16 || value == -500 || value == 42.42 || value == 'something' ) { // blah blah blah } I hate having all of those logical ORs strung together. I'm wondering if there is some kind of shorthand. Thanks! 回答1: var a = [1, 16, -500, 42.42, 'something']; var value = 42; if (a.indexOf(value) > -1){ // blah blah blah } Upd: Utility function sample as proposed in comments: Object.prototype.in = function(

问题 Is it a bad idea to overload &&, || or comma operator and Why? 回答1: I wouldn't overload operator&& or operator|| . Even if you define a class that gives rise to a Boolean algebra (finite sets, for example), it would probably be a better choice to overload operator& and operator| . The reason is that C++ programmers expect special semantics for operator&& and operator|| : they are short-circuited , i.e. don't evaluate their right-hand argument if not necessary. You can't get this behavior by