ternary-operator

问题 GCC has an awesome ternary expression extension to C which allows us to create a statement like this: int x = some_var ?: 10; // expands to some_var ? some_var : 10 Which is really nice, and while it's not particularly intuitive, it does work. Most binary operators in the C language have an additional operator associated with them, which allows for assignment: x = x + 2; // instead, we can say x += 2; Since this is the case, and the norm for most binary C operators ( + , - , * , / , % , | , &

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Python Ternary Operator Is there control flow operator similar to '?' of C/C++ in python? If there is a chunk of code similar to this: return n <= 1 ? n : fibo(n-1) + fibo(n-2) Will got an error like this: File "fibonacci.py", line 2 return n <= 1 ? n : fibo(n-1) + fibo(n-2) ^ SyntaxError: invalid syntax 回答1: Yes, the conditional expression is available in Python 2.5+: return n if n <= 1 else fibo(n-1) + fibo(n

问题 I often find myself needing to write code with the following logical pattern: $foo = isset($bar) ? $bar : $baz; I know about the ?: syntax: $foo = $bar ?: $baz; ...which, on the surface, appears to be what I'm looking for; however, it throws an undefined notice index when $bar is not set. It also uses the same logic as empty() , meaning that "empty" values like FALSE , 0 , "0" , etc. don't pass. Hence, it's not really equivalent. Is there a shorter way of writing that code without throwing a

问题 I implemented a ternary operator like Java's <condition> ? <if true> : <if false> , substituting / for : , since : is not a valid identifier: case class Ternary[T](val o: Option[T]) { def / (f: => T) = o getOrElse f } implicit def boolToTernary(cond: Boolean) = new { def ? [T](f: => T) = if(cond) Ternary(Some(f)) else Ternary[T](None) } It works fine in general, e.g. scala> (1 > 2) ? "hi" / "abc" res9: java.lang.String = abc but falls down in the following case: scala> (1 > 2) ? 5 / 6.0

问题 I was studying about ternary operation nesting and made some tests with this routine: <?php $test1 = [15,30,'ok']; $test2 = [8,90,'fail']; $test3 = [4,32,'ok']; $test1[2] == 'ok' ? print('First passed. The second round marks '. $test2[1]/$test2[0] < 10 ? 'an irrelevant value' : $test2[1]/$test2[0]. ' and the third was skipped.') : print('First failed. The second round was skipped and the third marks '. $test3[1]/$test3[0] < 10 ? 'an irrelevant value' : $test3[1]/$test3[0]); Although I know

问题 int m = 5, d = 12, y = 1975, val; // May 12, 1975 Can someone please explain the function/purpose of the comma operator in the line of code below: val = (d+=m<3?y--:y-2,23*m/9+d+4+y/4-y/100+y/400)%7; The above line was written by Mike Keith to calculate the day of the week given the date (d = day, m = month, y = year). Where Sunday = 0, Monday = 1, Tuesday = 2, Wednesday = 3, Thursday = 4, Friday = 5, Saturday = 6. I understand that the y-- gets executed if d+=m<3 is true, else the y-2 is

问题 This question already has answers here : Swift ternary operator compilation error (2 answers) Closed 2 years ago . I have an array of Doubles, and a button which when pressed empties the array. I want the button to be enabled only when the count of the array is greater than zero. The code is the following: var numbers: [Double] = [] //At some point I add some numbers here numbers.count > 0 ? deleteAllNumbersButton.isEnabled = true : deleteAllNumbersButton.isEnabled = false The compiler

问题 This question already has answers here : What is the Java ?: operator called and what does it do? (16 answers) Closed 6 years ago . I dont know what the question mark ( ? ) stand for in java, I was doing a small program, a Nim-game. were looking in a book, for help and saw this statement: int pinsToTake = (min >= 2) ? 2 : 1; I don't understand it, what will ? represent, can it be something to do with if-statement but you put it in a variable? and the : can be something "else"? (this things

问题 Regarding the ternary ( ? : ) operator in JavaScript, I would like to know how it is evaluated by a typical browser's JavaScript interpreter: Alternative A: Evaluate the first operand. If the result of the first operand is true, then evaluate and return the second operand. Else, evaluate and return the third operand. Alternative B: All three operands are evaluated. If the result of the first operand is true, return the result of the second operand. Else, return the result of the third operand

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