Tutorial by Examples: sin

When you make a subclass of a base class, you can construct the base class by using : base after the subclass constructor's parameters. class Instrument { string type; bool clean; public Instrument (string type, bool clean) { this.type = type; this.clean = c...

Print element at index 0 echo "${array[0]}" 4.3 Print last element using substring expansion syntax echo "${arr[@]: -1 }" 4.3 Print last element using subscript syntax echo "${array[-1]}" Print all elements, each quoted separately echo "${array[@...

2.0 Guard checks for a condition, and if it is false, it enters the branch. Guard check branches must leave its enclosing block either via return, break, or continue (if applicable); failing to do so results in a compiler error. This has the advantage that when a guard is written it's not possible ...

var favoriteColors: Set = ["Red", "Blue", "Green"] //favoriteColors = {"Blue", "Green", "Red"} You can use the insert(_:) method to add a new item into a set. favoriteColors.insert("Orange") //favoriteColors = {"Red&q...

from collections import Counter c = Counter(["a", "b", "c", "d", "a", "b", "a", "c", "d"]) c # Out: Counter({'a': 3, 'b': 2, 'c': 2, 'd': 2}) c["a"] # Out: 3 c[7] # not in the list (7 oc...

Import the ElementTree object, open the relevant .xml file and get the root tag: import xml.etree.ElementTree as ET tree = ET.parse("yourXMLfile.xml") root = tree.getroot() There are a few ways to search through the tree. First is by iteration: for child in root: print(child.ta...

Final classes When used in a class declaration, the final modifier prevents other classes from being declared that extend the class. A final class is a "leaf" class in the inheritance class hierarchy. // This declares a final class final class MyFinalClass { /* some code */ } ...

Python 3.2+ has support for %z format when parsing a string into a datetime object. UTC offset in the form +HHMM or -HHMM (empty string if the object is naive). Python 3.x3.2 import datetime dt = datetime.datetime.strptime("2016-04-15T08:27:18-0500", "%Y-%m-%dT%H:%M:%S%z"...

Parameters can be used for returning one or more values; those parameters are required to be non-const pointers or references. References: void calculate(int a, int b, int& c, int& d, int& e, int& f) { c = a + b; d = a - b; e = a * b; f = a / b; } Pointers: ...

C++11 The type std::tuple can bundle any number of values, potentially including values of different types, into a single return object: std::tuple<int, int, int, int> foo(int a, int b) { // or auto (C++14) return std::make_tuple(a + b, a - b, a * b, a / b); } In C++17, a braced init...

C++11 The container std::array can bundle together a fixed number of return values. This number has to be known at compile-time and all return values have to be of the same type: std::array<int, 4> bar(int a, int b) { return { a + b, a - b, a * b, a / b }; } This replaces c style ar...

There are several ways to extract characters from a std::string and each is subtly different. std::string str("Hello world!"); operator[](n) Returns a reference to the character at index n. std::string::operator[] is not bounds-checked and does not throw an exception. The caller is...

var fs = require('fs'); // Save the string "Hello world!" in a file called "hello.txt" in // the directory "/tmp" using the default encoding (utf8). // This operation will be completed in background and the callback // will be called when it is either done or fail...

Use Case CASE can be used in conjunction with SUM to return a count of only those items matching a pre-defined condition. (This is similar to COUNTIF in Excel.) The trick is to return binary results indicating matches, so the "1"s returned for matching entries can be summed for a count o...

The keyword 'using' has three flavors. Combined with keyword 'namespace' you write a 'using directive': If you don't want to write Foo:: in front of every stuff in the namespace Foo, you can use using namespace Foo; to import every single thing out of Foo. namespace Foo { void bar() {} ...

Explicitly closing a file is rarely necessary in C++, as a file stream will automatically close its associated file in its destructor. However, you should try to limit the lifetime of a file stream object, so that it does not keep the file handle open longer than necessary. For example, this can be ...

Normally a change of webpage within an Iframe is initiated from with the Iframe, for example, clicking a link inside the Ifame. However, it is possible to change an IFrame's content from outside the IFrame. You can use an anchor tag whose href attribute is set to the desired URL and whose target at...

The srcdoc attribute can be used (instead of the src attribute) to specify the exact contents of the iframe as a whole HTML document. This will yield an IFrame with the text "IFrames are cool!" <iframe srcdoc="<p>IFrames are cool!</p>"></iframe> If the...

Many databases allow to make the primary key value automatically increment when a new key is added. This ensures that every key is different. MySQL CREATE TABLE Employees ( Id int NOT NULL AUTO_INCREMENT, PRIMARY KEY (Id) ); PostgreSQL CREATE TABLE Employees ( Id SERIAL PRIMARY...

There are two primary ways of accessing elements in a std::vector index-based access iterators Index-based access: This can be done either with the subscript operator [], or the member function at(). Both return a reference to the element at the respective position in the std::vector (unles...