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Operations that return NaN

Mathematical operations on values other than numbers return NaN. "a" + 1 "b" * 3 "cde" - "e" [1, 2, 3] * 2 An exception: Single-number arrays. [2] * [3] // Returns 6 Also, remember that the + operator concatenates strings. "a" + "b&...

JavaScript • Built-in Constants

Math library functions that return NaN

Generally, Math functions that are given non-numeric arguments will return NaN. Math.floor("a") The square root of a negative number returns NaN, because Math.sqrt does not support imaginary or complex numbers. Math.sqrt(-1)

JavaScript • Built-in Constants

Testing for NaN using isNaN()

window.isNaN() The global function isNaN() can be used to check if a certain value or expression evaluates to NaN. This function (in short) first checks if the value is a number, if not tries to convert it (*), and then checks if the resulting value is NaN. For this reason, this testing method may ...

JavaScript • Built-in Constants

Blocks as Method Parameters

- (void)methodWithBlock:(returnType (^)(paramType1, paramType2, ...))name;

Objective-C Language • Blocks

Comparing Objects

In order to compare the equality of custom classes, you can override == and != by defining __eq__ and __ne__ methods. You can also override __lt__ (<), __le__ (<=), __gt__ (>), and __ge__ (>). Note that you only need to override two comparison methods, and Python can handle the rest (== ...

Python Language • Comparisons

Basic usage getting content between buffers and clearing

Output buffering allows you to store any textual content (Text, HTML) in a variable and send to the browser as one piece at the end of your script. By default, php sends your content as it interprets it. <?php // Turn on output buffering ob_start(); // Print some output to the buffer (via...

PHP • Output Buffering

Capturing the output buffer to re-use later

In this example, we have an array containing some data. We capture the output buffer in $items_li_html and use it twice in the page. <?php // Start capturing the output ob_start(); $items = ['Home', 'Blog', 'FAQ', 'Contact']; foreach($items as $item): // Note we're about to step &q...

PHP • Output Buffering

Running output buffer before any content

ob_start(); $user_count = 0; foreach( $users as $user ) { if( $user['access'] != 7 ) { continue; } ?> <li class="users user-<?php echo $user['id']; ?>"> <a href="<?php echo $user['link']; ?>"> <?php echo $user...

PHP • Output Buffering

Using Output buffer to store contents in a file, useful for reports, invoices etc

<?php ob_start(); ?> <html> <head> <title>Example invoice</title> </head> <body> <h1>Invoice #0000</h1> <h2>Cost: &pound;15,000</h2> ... </body> </html> <?php...

PHP • Output Buffering

Using the multiprocessing module to parallelise tasks

import multiprocessing def fib(n): """computing the Fibonacci in an inefficient way was chosen to slow down the CPU.""" if n <= 2: return 1 else: return fib(n-1)+fib(n-2) p = multiprocessing.Pool() print(p.map(fib,[38,37,3...

Python Language • Parallel computation

Ignore files that have already been committed to a Git repository

If you have already added a file to your Git repository and now want to stop tracking it (so that it won't be present in future commits), you can remove it from the index: git rm --cached <file> This will remove the file from the repository and prevent further changes from being tracked by...

Git • Ignoring Files and Folders

Basics of multithreading

Using the threading module, a new thread of execution may be started by creating a new threading.Thread and assigning it a function to execute: import threading def foo(): print "Hello threading!" my_thread = threading.Thread(target=foo) The target parameter references the fun...

Python Language • Multithreading

Defining and Assigning

A block that performs addition of two double precision numbers, assigned to variable addition: double (^addition)(double, double) = ^double(double first, double second){ return first + second; }; The block can be subsequently called like so: double result = addition(1.0, 2.0); // result =...

Objective-C Language • Blocks

Recorded (not live) Video Player

twitch • Interactive Embed Video Player

Loading and using a module

A module can be "imported", or otherwise "required" by the require() function. For example, to load the http module that ships with Node.js, the following can be used: const http = require('http'); Aside from modules that are shipped with the runtime, you can also require mod...

Node.js • Exporting and Consuming Modules

Creating a hello-world.js module

Node provides the module.exports interface to expose functions and variables to other files. The most simple way to do so is to export only one object (function or variable), as shown in the first example. hello-world.js module.exports = function(subject) { console.log('Hello ' + subject); }...

Node.js • Exporting and Consuming Modules

Limit and Offset relationship

Considering the following users table: idusername1User12User23User34User45User5 In order to constrain the number of rows in the result set of a SELECT query, the LIMIT clause can be used together with one or two positive integers as arguments (zero included). LIMIT clause with one argument When ...

MySQL • Limit and Offset

Italic

Italics can be created by surrounding text with either asterisks or with underscores: *Italicized text* _Also italicized_ Result: Italicized text Also italicized

Markdown • Text Formatting

Simple Category

Interface and implementation of a simple category on NSArray, named Filter, with a single method that filters numbers. It is good practice to add a prefix (PF) to the method to ensure we don't overwrite any future NSArray methods. @interface NSArray (PFFilter) - (NSArray *)pf_filterSmaller:(dou...

Objective-C Language • Categories

General Pattern that does most commonly asked about tasks

The following is how to properly use the java.util.Scanner class to interactively read user input from System.in correctly( sometimes referred to as stdin, especially in C, C++ and other languages as well as in Unix and Linux). It idiomatically demonstrates the most common things that are requested ...

Java Language • Scanner