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OC-collection class 1. the OC collection classes include nsarray, nsset, and nsdictionary. They all operate arrays in an object-oriented manner. Unlike arrays in C, OC Arrays can only store the same data type. They can store any type of objects, however, non-OC object types such as basic data types int, struct, and enum cannot be stored. 2. The OC array exists as an object. Therefore, you must add * 3. Once an nsarray array is created, it determines whether it is variable or not. 4. Basic ns

: the pear db module and the PHP Data Objects (PDO) class. Both provide abstraction from the choice of a specific database. Therefore, your code can run on IBM DB2, MySQL, PostgreSQL, or any other database you want to connect to without too much adjustment.Another value of using the pear db module and the PDO abstraction layer is that you can use it in SQL statements? Operator. This makes SQL easier to maintain and protects your applications from SQL injection attacks.The alternative code for us

Foreach is often used in PHP, and arrays must be used to use foreach. Therefore, in this article, we talk about arrays and foreach. Foreach is often used in PHP, and arrays must be used to use foreach. Therefore, in this article, we talk about arrays and foreach. Foreach has two syntaxes: First, traverse the given array statement array_expression array. In each loop, the value of the current unit is assigned to $ value and the pointer inside the array moves forward (so the next unit will be obt

execute the gzip or gunzip command tar to process the directory without deleting the source file. for example: tar-cvf/home/jack/dest.tar/home/jack/source package/home/jack/source into/home/jack/dest.tar-zcvf/home/jack/dest.tar.gz/ home/

When we use the "who" or "w" command on a Linux terminal, we will always see a long list of users. At this time, do you really want to send a message to him/her. If she is a long-time-honored MM, and you see her, she is also shy. Do you want to send a message to her and say "hello, you are also there ". Hey hey, are you looking forward to it? Let's introduce several commands to let you send them to her or him. Write: send messages to other users in the system. Usage: Write + User Name Write +

that in addition to the Comparable protocol, a protocol is defined _Comparable , and the former inherits from the latter. _Comparablethe agreement is defined as follows:protocol _Comparable { ... }func BoolWe found that just what we lost here was found. _Comparableis an example of the default protocol implementation mechanism provided in Swift. The _Comparable default implementations for several other operators are provided in the Protocol >=,>, .Since Comparable both the self _Comparable and

() function to create a set. Note: To create an empty set, you must use set () instead of {}, because {} is used to create an empty dictionary. >>> Student = {'Tom ', 'Jim', 'Mary ', 'Tom', 'Jack ', 'Rose'} >>> print (student) # repeated elements are automatically removed {'Jim ', 'jack', 'Mary', 'Tom ', 'Rose '}>>> 'Rose' in student # membership testing (member test) True >># set can perform set operation

parenthesis) ends. Each "name" is followed by a ":" (colon); "' Name/value ' pair ' is separated by", "(comma).Example: var json = {"name": "Jack", "age": All, "Marray": true};2. Ordered list of values (an ordered list of values). In most languages, it is understood as an array (array or List).An array is an ordered collection of values (value). An array begins with "[" (the left square bracket), and "]" (the right square bracket) ends. Use "," (comm

When we use the command "who" or "W" in Linux terminal, we always see a long list of users, at this time, you do not want to send a message to him/her. If she is a you love for a long time mm, and you just see her also in, under the shy of you, is not at this time want to send a message to her, say "Hello, you are in AH" or "gee, so coincidence."Hey, you are not very looking forward to the following to introduce a few commands, let you send to her or him .1. Write: Send a message to other users

Dark Horse programmer------1 Nsset and NsmutablesetNsset, like Nsarray, is also a collection, but multiple objects in the collection are not in the obvious order. Nsset does not allow the inclusion of the same elements, and if an attempt is made to place two identical elements in the same Nsset collection, only one element is preserved. Nsmutablearray represents a variable set of Nsset collection elements, adding and removing methods based on Nsset.The basic use of set is void Test () { /

indexed and sliced, the same method.3. Note the special syntax rules for constructing tuples that contain 0 or 1 elements.4, the tuple can also use the + operator for stitching. Five, Sets A collection (set) is a set of unordered, distinct elements. The basic function is to conduct member relationship testing and eliminate duplicate elements. You can use curly braces or set () functions to create set collections, note: Creating an empty collection must be set () instead of {} because {} is us

) # returns the smallest 5 values in the list Redis 127.0.0.1:6379> SORT rank LIMIT 0 5 1) "1 " 2 ) "2 " 3)" 3 " 4" "4" 5) "5" You can use multiple modifiers in combination. The following example returns the first 5 objects sorted from large to small. Redis 127.0.0.1:6379> SORT Rank LIMIT 0 5 DESC 1) "Ten" 2) "9" 3 ) "8" 4) "7" 5 ) "6" Iv. use external key to sort You can use the data of the external key as a weight instead of the default direct contrast key value to sort. Suppose yo

(1) Preparation environment 1) Create an employee tablemysql> create table company.employee6( -> emp_id int auto_increment primary key not null, -> emp_name varchar(10), -> age int, -> dept_id int);mysql> insert into employee6(emp_name,age,dept_id) values -> (‘tom‘,19,200), -> (‘jack‘,30,201), -> (‘alice‘,24,202), -> (‘robin‘,40,200), -> (‘natasha‘,28,204);2) Create a departmental tablemysql> create table company.department(