Beginners to learn PHP variables, constants, arrays, functions, php constants_PHP tutorial

Beginner to learn PHP variables, constants, arrays, functions, PHP constants

Recently I have learned some PHP, and continue to record notes for easy review later. The previous JS and Swift I took two days to find time to sort it out and improve it. PHP is not as ink-filled as before, so here’s the practical stuff.

PHP is a language that interacts with the server. It is object-oriented and I don’t want to talk about other features. To sum up, it is very popular now and very practical. There is nothing wrong with learning it.

Variable declaration in PHP

There is no clear type modifier in PHP, so the declared variable does not need to be given a type like other languages, or even just a var. In PHP, variables are represented by $ as an identifier, and the rest of the features are the same as JS Very similar, there is no type, the type can be changed, and everything is legal.

　$string = "JianweiWang"; //Declare a variable

$string = 5; //Modify the value of $string to 5, legal

echo $string; //5, the print result is 5

The naming rules for variable names are quite similar to those in other languages. On the basis of the $ sign, the letter starts with an underscore, and the composition can only include numbers and letters underline (/w/ in regular expressions). In the variable name No spaces allowed, case sensitive. ($_name, $name, $name1, these are all legal).

Let’s talk about the empty types in PHP, null, NULL, variables destroyed using unset, the final type will be unified to NULL.

Constant declaration in PHP

Constants play a very important role in the robustness of a program. There will be no unsafe factors such as variable reassignment due to unclear variable names due to the change of project.

PHP does not have special modifiers for constants like in other languages, or uses closures to declare a constant in js, but has special function methods to define constants.

define("PI", 3.14, true);

Three parameters, the first parameter is the name of the constant, which requires a string type, the second parameter is the value of the constant, and the third parameter is whether it is case-sensitive. If set to true, it is not Sensitive, the default is false, generally no one is so boring and insensitive - -.

So the above statement is a constant with a value of 3.14. It is not allowed to be modified. Of course, the name cannot have the $ mark, and true is set, so this constant can be accessed using PI, or it can be pI.

Sometimes, in order to prevent a constant from being redefined, we need to test whether the constant exists, so we need to use another method. defined(), the parameter is a constant name string, and the return value is a bool type. Not much to say. Got...

Array

Array is a form of data collection, and it is still a normal old rule. Here is a brief introduction. The method will be added later. There are generally two ways to define an array in PHP. One is to use the array constructor. One is the literal form.

array constructor

　$array = array(1, 2, 3, 4, 5);

Literal form

　$array = [1, 2, 3, 4, 5];

Everything is clearer in PHP arrays (there seems to be no dictionary, because associative arrays can be used), the relationship between key and value is more obvious than in JS, and the index can be modified, rather than just traditional 0, 1, 2, 3. This is also an associative array.

Initialization of associative array

There are still two methods, constructor and literal.

Type constructor

$fruit = array(
'apple' => "apple",
'banana' => "banana",
'pineapple' => "pineapple"
) ;

Literal

　$fruit = [

　'apple' => "apple",
'banana' => "banana",
'pineapple' => "pineapple"

　];

Doesn’t this look like a dictionary? The access here is the same as JS, accessed through key values.

print_r($fruit['apple']); //You can get apples here.

Generally, the foreach method is used to traverse an array. Here is a brief introduction. You can write more by yourself.

foreach($fruit as $key => $value){

echo $key.$value.'
';

　}

This will print out

Apple apple

Banana

pineapple pineapple

Function

A function encapsulates a piece of code that can be reused, and can be called repeatedly in future use, improving the readability of the code. This is the same as in other languages, so I won’t go into details. The main points are Different ones, such as parameter tables and the like.

Function func(){};

In PHP, this is also the basic structure of a function, but it is different from some uses of JS, such as implicit triggering, etc., but the function name string is assigned to the variable name, and then triggered through the variable name. Functions, these are still very similar to the underlying implementation.

Function method(){

echo "wang";

　}

　$func = "method"; //Give the method() method to the variable $func

mechod(); //Call the method() method

$func(); //Calling $func also calls method(). This method is called a variable function

PHP has a large number of built-in functions, so I won’t go into details.

　

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