switch-statement

问题 Is there a way in Javascript to compare one integer with another through switch case structures without using if statements? E.g. switch(integer) { case 1 to 10: break; case 11 to 20: break; case 21 to 30: break; } 回答1: You can do some math manipulations. switch(Math.ceil(integer/10)) { case 1: // Integer is between 1-10 break; case 2: // Integer is between 11-20 break; case 3: // Integer is between 21-30 break; } 回答2: There is a way, yes. I'm pretty sure I'd use an if/else structure in my

问题 I am using SWITCH (like android toggle button ) instead of normal buttons in my andorid app. The code works fine while enabling and disabling switches. But i want to store the state of the switch. Suppose i enable the switch and close my application the background code will run fine but the switch state will change to disabled. Every time when i close the application the switch state becomes disabled. Is there any way to store the switch State?? 回答1: Use shared preferences or a database to

问题 I don't understand what's happening here. Logically, it doesn't make any sense to me. <?php $level = 0; switch ($level) { case $level > 80: $answer = 'high'; break; case $level > 60: $answer = 'moderate-to-high'; break; case $level > 40: $answer = 'moderate'; break; case $level > 20: $answer = 'low-to-moderate'; break; default: $answer = 'low'; break; } echo $answer; ?> When $level == 0, it returns "high". This doesn't make any sense to me. Can someone explain what's happening here? 回答1:

问题 Why is it not possible to use enum values as strings in a switch case? (Or what is wrong with this:) String argument; switch (argument) { case MyEnum.VALUE1.toString(): // Isn't this equal to "VALUE1" ? // something break; case MyEnum.VALUE2.toString(): // something else break; 回答1: You can only use strings which are known at compile time. The compiler cannot determine the result of that expression. Perhaps you can try String argument = ... switch(MyEnum.valueOf(argument)) { case VALUE1: case

问题 I'd like to know if there is any efficiency difference between using if statement or switch. For example: if(){ //code } else if(){ //code } else{ //code } I believe that program needs to go and check all of the if statement even if the first if statement was true. switch(i){ case 1: //code break; case 2: //code break; But in the switch, there is a break command. Is my approaching right? If not, could you explain the efficiency difference between them? 回答1: Switch perf is better than if else

问题 In the official Swift Programming Language guide, it has this to say about switch case: "...if the case contains multiple patterns that match the control expression, none of those patterns can contain constant or variable bindings." What does it mean by containing multiple patterns? 回答1: It means that case labels with multiple patterns cannot declare variables. This is allowed: let somePoint = (1, 1) switch somePoint { // Case with multiple patterns without binding case (0, _), (_, 0):

问题 I have 4 buttons that call one function. Depending on which button was pressed i need to hide button inside of function that called after pressing.I dont know which button was pressed so i tried to assign tags for each of 4 buttons to identify them by tag and use switch I tried this switch sender.tag { case 1: self.button1.hidden = true case 2: self.button2.hidden = true case 3: self.button3.hidden = true case 4: self.button4.hidden = true } but this doesnt work compiler says about use of

问题 final int a = 1; final int b; b = 2; final int x = 0; switch (x) { case a:break; // ok case b:break; // compiler error: Constant expression required } /* COMPILER RESULT: constant expression required case b:break; ^ 1 error */ Why am I getting this sort of error? If I would have done final int b = 2 , everything works. 回答1: b may not have been initialized and it is possible to be assigned multiple values. In your example it is obviously initialized, but probably the compiler doesn't get to

问题 I can't figure out how to use switches in combination with an enum. Could you please tell me what I'm doing wrong, and how to fix it? I have to use an enum to make a basic calculator. public enum Operator { PLUS, MINUS, MULTIPLY, DIVIDE } public double Calculate(int left, int right, Operator op) { int i = (int) op; switch(i) { case 0: { return left + right; } case 1: { return left - right; } case 2: { return left * right; } case 3: { return left / right; } default: { return 0.0; } } } The end

问题 I'm writing code for a sortable table, where clicking the links in the header change the ORDER BY executed when generating a set of search results (the case where there there is no valid order by causes the query to not be run with order by and just return the results in the order the database returns. this is as designed). The code is being written within a framework provided by my employer. To validate the ORDER BY part of the query I run the input through the following validation function.