operators

问题 What does the &= operator mean in Python, and can you give me a working example? I am trying to understand the __iand__ operator. I just don't know what &= means and have looked online but couldn't find it. 回答1: Explanation Understandable that you can't find much reference on it. I find it hard to get references on this too, but they exist. The i in iand means in-place , so it's the in-place operator for & . &= calls the __iand__ operator, if it is implemented. If not implemented, it is the

问题 This question already has answers here : Undefined behavior and sequence points (5 answers) Behavior of post increment in cout [duplicate] (4 answers) Closed 13 days ago . I'm having trouble understanding how Post Increment (++), Pre Increment work together in an example. x++ means add 1 to the variable But I am confused with this example: using namespace std; / run this program using the console pauser or add your own getch, system("pause") or input loop */ int main() { int a; a=8; cout<<++a

问题 This question already has answers here : How to combine two strings together in PHP? (17 answers) Reference — What does this symbol mean in PHP? (20 answers) Closed 12 months ago . Why does the following code output 0? It works with numbers instead of strings just fine. I have similar code in JavaScript that also works. Does PHP not like += with strings? <?php $selectBox = '<select name="number">'; for ($i=1; $i<=100; $i++) { $selectBox += '<option value="' . $i . '">' . $i . '</option>'; }

问题 This question already has answers here : How to combine two strings together in PHP? (17 answers) Reference — What does this symbol mean in PHP? (20 answers) Closed 12 months ago . Why does the following code output 0? It works with numbers instead of strings just fine. I have similar code in JavaScript that also works. Does PHP not like += with strings? <?php $selectBox = '<select name="number">'; for ($i=1; $i<=100; $i++) { $selectBox += '<option value="' . $i . '">' . $i . '</option>'; }

问题 This is the new assignment operator I see in Flutter source code: splashFactory ??= InkSplash.splashFactory; textSelectionColor ??= isDark ? accentColor : primarySwatch[200]; what's the meaning of this assignment operator? example in Flutter source code 回答1: ??= is a new null-aware operators. Specifically ??= is null-aware assignment operator. ?? if null operator. expr1 ?? expr2 evaluates to expr1 if not null , otherwise expr2 . ??= null-aware assignment. v ??= expr causes v to be assigned

问题 This is the new assignment operator I see in Flutter source code: splashFactory ??= InkSplash.splashFactory; textSelectionColor ??= isDark ? accentColor : primarySwatch[200]; what's the meaning of this assignment operator? example in Flutter source code 回答1: ??= is a new null-aware operators. Specifically ??= is null-aware assignment operator. ?? if null operator. expr1 ?? expr2 evaluates to expr1 if not null , otherwise expr2 . ??= null-aware assignment. v ??= expr causes v to be assigned

问题 This is a question I've always pondered on and have never found any resource stating the answer to this question. In fact its not only for += , but also for its siblings i.e. -= , *= , /= , etc. (of course not == ). Consider the example, int a = 5; a += 4; //this will make 'a' 9 Now consider the equivalent expression: a = a + 4; //This also makes 'a' 9 If += were simply a shorthand for a = a + <rhs of +=> overloading + operator should also implicitly overload += , unless explicitly overloaded

问题 PowerShell has a pretty good built-in help system that I use a lot and I'm able to see all help options with Get-Help * and query Cmdlets or can look up Topics with Get-Help about_* and then say Get-Help about_compar* to open the Comparison Operators topic which is all very good. However, I was trying to find how to get help on the various string operators, like .replace, .compare, .split, .substring. Does anyone know how to pull these topics up on the PowerShell console (possibly, they might

问题 PowerShell has a pretty good built-in help system that I use a lot and I'm able to see all help options with Get-Help * and query Cmdlets or can look up Topics with Get-Help about_* and then say Get-Help about_compar* to open the Comparison Operators topic which is all very good. However, I was trying to find how to get help on the various string operators, like .replace, .compare, .split, .substring. Does anyone know how to pull these topics up on the PowerShell console (possibly, they might

问题 I need to use the OR operator in a jQuery if statement to filter out 10 states. My code works wile only excluding one state, but fails when i try to include multiple states. Is there a correct way to do this? Code I am am using : if ((state != 10) || (state != 15) || (state != 19) || (state != 22) || (state != 33) || (state != 39) || (state != 47) || (state != 48) || (state != 49) || (state != 51)) return true; Thanks 回答1: Think about what if ((state != 10) || (state != 15) || (state != 19) |