conditional-statements | 易学教程

Variable scope and order of parsing vs. operations: Assignment in an “if”

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问题 My understanding is that the if statements at the end of the line are evaluated before the code at the front of the line: 'never shown' if (false) And assignment is possible in an if statement. 'shown' if (value = 'dave is king') value #=> "dave is king" And, when a variable that doesn't exist is assigned to, it is created. There is no need for it to exist beforehand. Is this true? If all these assumptions are true, why does this fail? error_array << error if (error = import_value(value)) #=>

Replace negative values by zero

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We want to set all values in an array zero that are negative. I tried out a a lot of stuff but did not yet achieve a working solution. I thought about a for loop with condition, however this seems not to work. #pred_precipitation is our array pred_precipitation <-rnorm(25,2,4) for (i in nrow(pred_precipitation)) { if (pred_precipitation[i]<0) {pred_precipitation[i] = 0} else{pred_precipitation[i] = pred_precipitation[i]} } Thanks for the reproducible example. This is pretty basic R stuff. You can assign to selected elements of a vector (note an array has dimensions, and what you've given is a

Simpler way to check if variable is not equal to multiple string values?

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问题 Current Codes: <?php // See the AND operator; How do I simplify/shorten this line? if( $some_variable !== 'uk' && $some_variable !== 'in' ) { // Do something } ?> And: <?php // See the OR operator; How do I simplify/shorten this line? if( $some_variable !== 'uk' || $some_variable !== 'in' ) { // Do something else } ?> Is there a simpler (i.e. shorter) way to write the two conditions? NOTE: Yes, they are different, and I am expecting different ways to shorten the codes. 回答1: For your first

Angular JS - ng-repeat and loop conditions

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问题 Hey i have this piece of code: <div ng-repeat="i in values"> {{i}} </div> It works but i would like to put extra conditions inside the loop something like: <div ng-repeat="i in values"> {{i}} if(i !== 0){ <div></div> } </div> How can i achieve this? 回答1: Use ng-if (or ng-show ): <div ng-repeat="i in values"> <div ng-if="i !== 0"></div> </div> Attached to the element, this will decide whether to display it or not. Documentation for ng-if can be found here. However, if you want to only do

Switch statement using or

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问题 I'm creating a console app and using a switch statement to create a simple menu system. User input is in the form of a single character that displays on-screen as a capital letter. However, I do want the program to accept both lower- and upper-case characters. I understand that switch statements are used to compare against constants, but is it possible to do something like the following? switch(menuChoice) { case ('q' || 'Q'): //Some code break; case ('s' || 'S'): //More code break; default:

IN Clause with NULL or IS NULL

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Postgres is the database Can I use a NULL value for a IN clause? example: SELECT * FROM tbl_name WHERE id_field IN ('value1', 'value2', 'value3', NULL) I want to limit to these four values. I have tried the above statement and it doesn't work, well it executes but doesn't add the records with NULL id_fields. I have also tried to add a OR condition but this just make the query run and run with no end in sight. SELECT * FROM tbl_name WHERE other_condition = bar AND another_condition = foo AND id_field IN ('value1', 'value2', 'value3') OR id_field IS NULL Any suggestions? Daniel A. White An in

Find maximum of three number in C without using conditional statement and ternary operator

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I have to find maximum of three number provided by user but with some restrictions. Its not allowed to use any conditional statement. I tried using ternary operator like below. max=(a>b?a:b)>c?(a>b?a:b):c But again its restricted to use ternary operator. Now I am not getting any idea how to do this? Nawaz Taking advantage of short-circuiting in boolean expressions: int max(int a, int b, int c) { int m = a; (m < b) && (m = b); //these are not conditional statements. (m < c) && (m = c); //these are just boolean expressions. return m; } Explanation: In boolean AND operation such as x && y , y is

Check for equality in Spacebars?

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问题 I am trying to do what I think should be a very simple task, but have been failing to do so in the past hour. I want to select a select option by default if the user property matches the value. <select name="myName"> {{#each addKeys myTable}}  <option value="{{key}}" {{#if currentUser.property === key}}selected="selected"{{/if}}>{{value}}</option> {{/each}} </select> Now I thought this was straightforward enough to be implemented. But it

Using Action dictionaries instead of switch statements

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问题 I'm just reviewing some of my old code (have some spare time), and I noticed a rather lengthy switch statement. Due to gaining new knowledge, I have since refactored it in the following form: private Dictionary<string, Action> createView { get { return new Dictionary<string, Action>() { {"Standard", CreateStudySummaryView}, {"By Group", CreateStudySummaryByGroupView}, {"By Group/Time", CreateViewGroupByHour} }; } } Would you consider this good practise, or is this simply a case of being

Triggering jquery with css media queries

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I am using css media queries on my project to create a site that will work with any sized screen. I am looking to trigger difference jquery functions just like I would with css. For example, If the browser size is between 1000px and 1300px, I would like to call the following function: $('#mycarousel').jcarousel({ vertical: true, scroll: 1, auto: 2, wrap: 'circular' }); BUT when the browser size is below 1000px, the js would stop its processing. So on and so forth. I'm not sure if this is possible, but perhaps there is an existing solution or plugin that creates different js environments based