PHP study notes

Introduction of PHP

PHP (full name: PHP: Hypertext Preprocessor) is an open source general-purpose computer scripting language, especially suitable for web development and embedded in HTML. The syntax of PHP draws on the characteristics of popular computer languages such as C language, Java and Perl, and is easy for general programmers to learn. The main goal of PHP is to allow web developers to quickly write dynamic pages, but PHP is also used in many other areas.

The PHP file extension is .php, E.g index.php. As mentioned above, PHP can directly embed HTML.

Usage

When the browser reads <?php from top to bottom, it executes PHP and ends with ?>. Such as:

<!DOCTYPE html>
<html>
    <head>
        <title>PHP</title>
    </head>
    <body>
        <?php
            echo "This is a sentence."
        ?>
    </body>
</html>

Precautions

In PHP, there is no other HTML after the PHP directive is completed. It is recommended not to end with ?>. It will cause trouble if it is closed.

<?php
    echo "No HTML after PHP ends";

PHP comments

Almost most web programming languages can comment, and the single-line way of PHP is // and the multi-line way is /* Some text here */.

<?php
    echo = "This is a single line comment"; // I am a single line comment
    echo = "This is a multi-line comment";
    /*
        I am a multi-line comment
        Second line
    */
?>

Echo

The simplest syntax in PHP is Echo. The content of Echo must be enclosed in double quotes "" or single quotes ''. Each syntax must end with a semicolon ;.

<?php
    echo "This is the example of using double quotes.";
    echo 'This is the example of using single quotes.';
?>

Content in Echo can also use HTML syntax. For example, I used <br/> here, so that the line can be broken.

<?php
    echo "This is the first sentence<br/>";
    echo "This is the second sentence";
    echo "<a href=\"https://example.com\">here is a link</a>";
?>

Variable

We can assign a value to a variable to make it easier for us to write PHP, similar to Javascript. We will use the Dollar sign $.

<?php
    $value = "I am a value";
?>

There are some rules to follow when we name variables.

Example	Description	Rules
$value	Lowercase	✅
$Value	Uppercase	✅
$_value	Underscore	✅
$1value	Start from number	❌

There is a difference between uppercase and lowercase in variable names. Uppercase variables are not equal to lowercase variables.

Variable Naming Tips

Camel case

When a variable name and a function name are linked together by two or more words to form a unique identification word, the use of "camel case" to represent, can increase the readability of variables and functions. Because we can't have spaces in variables.

<?php
    $onePlusOneAnswer = 1 + 1;
    echo $onePlusOneAnswer;
?>

Snake case

Snake case (like snake_case) refers to a writing style in which every space is replaced with an underscore ( _ ) character and the first letter of every word is written in lowercase.

<?php
    $one_plus_one_answer = 1 + 1;
    echo $one_plus_one_answer;
?>

String operator

There are two string operators. The first is the concatenation operator ("."), which returns the concatenated string of its left and right arguments. The second is the concatenation assignment operator (".="), which appends the right-hand argument to the left-hand argument.

<?php
    echo "This" . " " . "is" . " " . "String" . " " . "operators" . ".";
?>

Arithmetic operator

<?php
    $value0 = 1.5 // Float
    $value1 = 1 + 1 // Plus
    $value2 = 1 - 1 // Minus
    $value3 = 1 * 1 // Times
    $value4 = 1 / 1 // Divide
    $value5 = 12 / 5 // Divide | Incomplete division will become float, which is different from other programming languages, php will calculate the remainder
    $value6 = 3 % 5 // take the remainder
?>