9.3.1. Swift introduction #

We can use it. import statement to introduce any Objective-C framework (or C library) into the Swift program. For example import cocoa statement is imported using the Cocoa library and API, which we can use in Swift programs.

Cocoa itself is written by Objective-C language, and Objective-C is a strictsuperset of C language, so in Swift applications we can easily mix C language code, even C++ code.

9.3.2. Swift marker #

The Swift program consists of a variety of tags, which can be words, identifiers, constants, strings or symbols. For example, the following Swiftprogram consists of three tags:

print("test!")

The above statement consists of three symbols: word ( print ), symbol ( ( ), string ( "test" ).

print
(
   "test!"
)

9.3.3. Annotation #

Swift comments are very similar to the C language, with single-line commentsbeginning with two backslashes:

//This is a line of comments

Multiline comments to / start with / end:

/* This is also a comment，
But spanning multiple lines */

Unlike multiline comments in the C language, multiline comments for Swift can be nested within other multiline comments. It is written by inserting another multiline comment within a multiline comment block. When the second comment block is closed, it is still followed by the first comment block:

/*This is the beginning of the first multiline comment
/*This is the second nested multiline comment*/
This is the end of the first multi line comment*/

The nesting of multi-line comments allows you to comment blocks of code morequickly and easily, even if there are already comments in the block.

9.3.4. semicolon #

Unlike other languages, Swift does not require a semicolon (;) at the end ofeach line of statements, but when you write multiple statements in the sameline, you must separate them with a semicolon:

import Cocoa
/* My first Swift program */
var myString = "Hello, World!"; print(myString)

9.3.5. Identifier #

Identifiers are names assigned to variables, constants, methods, functions, enumerations, structures, classes, protocols, and so on. There are certain norms for the letters that make up identifiers, and the naming rules for identifiers in Swift are as follows:

• Case sensitive, Myname and myname are two different identifiers

• The first character of an identifier can start with an underline (_) or a letter, but cannot be a number;

• Other characters in the identifier can be underscores (_), letters, or numbers.

For example: userName 、 User_Name 、 _sys_val , height, etc. are legal identifiers, while 2mail 、 room# and class is an illegal identifier.

Note: the letters in Swift are encoded by Unicode [1] . Unicode is called unified coding system, which contains Asian characters such as Chinese, Japanese, Korean and even emoticons that we use in chat tools.

If you must use a keyword as an identifier, you can add an accent (`) beforeand after the keyword, for example:

let `class` = "Runoob"

9.3.6. Keyword #

Keywords are reserved character sequences similar to identifiers and cannot be used as identifiers unless they are enclosed in an accent (`). Keywords are predefined reserved identifiers that have a special meaning to the compiler. There are four common keywords.

9.3.7. Keywords related to the declaration #

9.3.8. Keywords related to statements #

9.3.9. Expression and type keywords #

9.3.10. Keywords used in a particular context #

9.3.11. Swift Spac #

Swift language does not completely ignore spaces like C/C++ or Java. Swift has certain requirements for the use of spaces, but it is not as strict as Python’s requirements for indentation.

In Swift, operators cannot follow variables or constants directly. For example, the following code reports an error:

let a= 1 + 2

The error message is:

error: prefix/postfix '=' is reserved

It probably means that the equal sign comes directly before or after it. This usage is reserved.

The following code still reports an error (continue to pay attention to the spaces):

let a = 1+ 2

The error message is:

error: consecutive statements on a line must be separated by ';'

This is because Swift thinks that the statement is over by 1 +, and 2 is thenext statement.

Only by writing in this way will you not make a mistake:

let a = 1 + 2;  // This writing method is recommended for coding specifications
let b = 3+4 // This is also okay

9.3.12. Swift literal quantity #

A literal quantity is a value such as a specific number, string, or Boolean value that can directly indicate its own type and assign a value to a variable. For example, in the following:

42//integer literal
3.14159//Floating-point literal
Hello, world! "//String literal
True//Boolean literal

9.3.13. Printout #

Swift usage print function printout:

print("Runoob") // output Runoob

print the function is a global function, and the complete function signature is:

public func print(items: Any..., separator: String = default, terminator: String = default)

If we want it not to wrap, we just need to assign the last parameter to an empty string:

for x in 0...10{
    print("\(x) ", terminator: "")
}
print()

The output is as follows:

0 1 2 3 4 5 6 7 8 9 10

If you need to receive user input, you can use the readLine() :

let theInput = readLine()