PHP is a scripting language for back-end development. Its basic syntax includes four core parts: 1. PHP tags are used to define the code scope, the most common one is <?php ... ?>. If all files are PHP code, close tags can be omitted to avoid errors; 2. Variables start with $ and do not need to declare types. They support data types such as strings, integers, floating point numbers, booleans, arrays and objects, and can be cast through (int) and (string), etc. The scope of the variable is local by default. Global must be used to access global variables; 3. The control structure includes if/else condition judgment and for and foreach loops, which are used to implement program logic and repeated task processing; 4. Functions are used to encapsulate code to improve reusability, support parameter default values and return type declarations starting from PHP 7. The rational use of functions can make the code clearer and easier to maintain. After mastering these basic syntax, you can write a simple PHP program, but in actual applications, you need to pay attention to details such as variable scope and type conversion.

PHP is a scripting language widely used in back-end development. It syntactically draws on some features of C, Java and Perl, but has also been simplified to make it easier to get started. If you are new to PHP, mastering the basic syntax is the first step.

1. PHP tag: where to start and where to end

PHP code must be written between specific tags, the most common tag is <?php ... ?> . The server will parse the content between this tag as PHP code, while the content outside the tag is output as it is (such as HTML).

For example:

 <?php
echo "Hello, world!";
?>

It should be noted that if the file is full of PHP code, you can omit the closed tag ?> , which can avoid the "headers already sent" error caused by accidentally adding spaces or line breaks after the tag.

2. Variables and data types: Flexible use of dynamic types

PHP is a weak-type language. Variables do not need to declare their types in advance. You can define variables with the $ symbol:

 $name = "Tom";
$age = 25;
$isStudent = true;

Common data types include strings, integers, floating point numbers, booleans, arrays, and objects. Variable types can be automatically converted based on assignment, but casting is also supported:

• (int) or intval() to integer
• (string) convert to string
• (bool) converted to boolean

Pay attention to the scope of variables. By default, it is a local scope inside the function. To access global variables, you need to use the global keyword.

3. Control structure: Let the program run logically

PHP supports common control statements, such as conditional judgment and looping.

If/else judgment example:

 if ($age >= 18) {
    echo "adult";
} else {
    echo "minor";
}

Looping commonly used for and foreach:

 for ($i = 0; $i < 5; $i ) {
    echo $i;
}

$fruits = [&#39;apple&#39;, &#39;banana&#39;, &#39;orange&#39;];
foreach ($fruits as $fruit) {
    echo $fruit;
}

These structures can help you handle repetitive tasks or execute different codes according to different situations, and are the basis for building complex logic.

4. Function definition: encapsulate code to improve reusability

Functions are the basic unit of organizing code. You can define functions yourself or use built-in functions.

Examples of custom functions:

 function greet($name) {
    return "Hello, " . $name;
}

echo greet("Alice");

Function parameters can be set to default values:

 function saysHi($name = "Guest") {
    echo "Hi, " . $name;
}

Starting with PHP 7, return type declarations are also supported:

 function add(int $a, int $b): int {
    return $a $b;
}

Using functions reasonably can make the code clearer and easier to maintain.

Basically that's it. After mastering these basic syntax, you can try writing a simple PHP program. Although it doesn't seem complicated, details are easily overlooked in actual projects, especially in terms of variable scope and type conversion. It is recommended to write more examples to deepen your understanding.

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