Tutorial by Examples: e

do './config.pl'; This will read in the contents of the config.pl file and execute it. (See also: perldoc -f do.) N.B.: Avoid do unless golfing or something as there is no error checking. For including library modules, use require or use.

require Exporter; This will ensure that the Exporter module is loaded at runtime if it hasn't already been imported. (See also: perldoc -f require.) N.B.: Most users should use modules rather than require them. Unlike use, require does not call the module's import method and is executed at runti...

use Cwd; This will import the Cwd module at compile time and import its default symbols, i.e. make some of the module's variables and functions available to the code using it. (See also: perldoc -f use.) Generally this is will do the right thing. Sometimes, however, you will want to control whic...

Double click on the Main.Storyboard file. Set View As to iPhone 6: Drag a label and a button from the Toolbox to the design surface so that it looks like the image below: In the Properties pad, give the label and button the following properties: nothingNameTitleLabellblClicks[blank]Buttoncli...

When multi-line (?m) modifier is turned off, ^ matches only the input string's beginning: For the regex ^He The following input strings match: Hedgehog\nFirst line\nLast line Help me, please He And the following input strings do not match: First line\nHedgehog\nLast line IHedgehog ...

If you need to use the ^ character in a character class (Character classes ), either put it somewhere other than the beginning of the class: [12^3] Or escape the ^ using a backslash \: [\^123] If you want to match the caret character itself outside a character class, you need to escape it: ...

To conditionally include a block of code, the preprocessor has several directives (e.g #if, #ifdef, #else, #endif, etc). /* Defines a conditional `printf` macro, which only prints if `DEBUG` * has been defined */ #ifdef DEBUG #define DLOG(x) (printf(x)) #else #define DLOG(x) #endif Norm...

The most common uses of #include preprocessing directives are as in the following: #include <stdio.h> #include "myheader.h" #include replaces the statement with the contents of the file referred to. Angle brackets (<>) refer to header files installed on the system, while q...

The simplest form of macro replacement is to define a manifest constant, as in #define ARRSIZE 100 int array[ARRSIZE]; This defines a function-like macro that multiplies a variable by 10 and stores the new value: #define TIMES10(A) ((A) *= 10) double b = 34; int c = 23; TIMES10(b); //...

If the preprocessor encounters an #error directive, compilation is halted and the diagnostic message included is printed. #define DEBUG #ifdef DEBUG #error "Debug Builds Not Supported" #endif int main(void) { return 0; } Possible output: $ gcc error.c error.c: error: #e...

Swift's built-in numeric types are: Word-sized (architecture-dependent) signed Int and unsigned UInt. Fixed-size signed integers Int8, Int16, Int32, Int64, and unsigned integers UInt8, UInt16, UInt32, UInt64. Floating-point types Float32/Float, Float64/Double, and Float80 (x86-only). Literal...

func doSomething1(value: Double) { /* ... */ } func doSomething2(value: UInt) { /* ... */ } let x = 42 // x is an Int doSomething1(Double(x)) // convert x to a Double doSomething2(UInt(x)) // convert x to a UInt Integer initializers produce a runtime error if the value ove...

Use String initializers for converting numbers into strings: String(1635999) // returns "1635999" String(1635999, radix: 10) // returns "1635999" String(1635999, radix: 2) // returns "110001111011010011111&...

The searched CASE returns results when a boolean expression is TRUE. (This differs from the simple case, which can only check for equivalency with an input.) SELECT Id, ItemId, Price, CASE WHEN Price < 10 THEN 'CHEAP' WHEN Price < 20 THEN 'AFFORDABLE' ELSE 'EXPENSIVE' E...

Indexes can have several characteristics that can be set either at creation, or by altering existing indexes. CREATE CLUSTERED INDEX ix_clust_employee_id ON Employees(EmployeeId, Email); The above SQL statement creates a new clustered index on Employees. Clustered indexes are indexes that dict...

UPDATE Customers SET Email = "[email protected]" WHERE id = 1; This will fail if an unique index is set on the Email column of Customers. However, alternate behavior can be defined for this case: UPDATE Customers SET Email = "[email protected]" WHERE id = 1 ON DUP...

You define a class like this: class Dog {} A class can also be a subclass of another class: class Animal {} class Dog: Animal {} In this example, Animal could also be a protocol that Dog conforms to.

Classes are reference types, meaning that multiple variables can refer to the same instance. class Dog { var name = "" } let firstDog = Dog() firstDog.name = "Fido" let otherDog = firstDog // otherDog points to the same Dog instance otherDog.name = "Rover" // modifying otherDog also...

Classes can define properties that instances of the class can use. In this example, Dog has two properties: name and dogYearAge: class Dog { var name = "" var dogYearAge = 0 } You can access the properties with dot syntax: let dog = Dog() print(dog.name) print(dog.dogYear...

Templating can also be applied to functions (as well as the more traditional structures) with the same effect. // 'T' stands for the unknown type // Both of our arguments will be of the same type. template<typename T> void printSum(T add1, T add2) { std::cout << (add1 + add2) &...