PHP functions can improve code reusability and organization through function keyword definition. 1. Use function function name (parameter list) when defining a function { function body return return value; }, such as function add($a, $b) { return $a $b; }, the function name is case-sensitive, the parameters can have multiple or none, return is optional. 2. When calling a function, you must use the function name to add brackets and pass in the corresponding parameters, such as $result = add(3, 5); and the parameter order should be consistent with the definition, and brackets cannot be omitted. 3. You can set default parameters to enhance flexibility, such as function greet($name = "Guest") { echo "Hello, $name!"; }, which can be omitted when calling. 4. It is recommended to store functions in separate files and introduce them through include or require to avoid repeated definitions. You can use function_exists() to check whether they have been defined and the naming should be clear and clear.

It is actually not difficult to define and call a PHP function. As long as you understand the basic structure and syntax, you can get started quickly. Functions are the basic tools for organizing code and improving reusability. Whether writing small projects or large applications, they are inseparable from them.

1. How to define a function?

PHP uses the function keyword to define functions. The basic format is as follows:

 function function name (parameter list) {
    // Function body, that is, the executed code return return value; // optional}

For example, define a simple addition function:

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

Some points to note:

• Function names are case-insensitive (but they are recommended to remain consistent)
• There can be multiple parameters or no
• return is an optional option to return the result

2. How to call a function?

After defining the function, you only need to use the function name to add brackets and pass in the corresponding parameters to call:

 $result = add(3, 5);
echo $result; // Output 8

Pay attention to when calling:

• The parameter order must be consistent with the definition
• If the parameter type is expected in the function, try to pass the correct type of data as much as possible
• Parentheses cannot be saved when calling a function without parameters

3. Use default parameters to make functions more flexible

Sometimes we want certain parameters to have default values ??so that they can be optionally omitted when called. For example:

 function greet($name = "Guest") {
    echo "Hello, $name!";
}

The call method can be:

 greet(); // Output Hello, Guest!
greet("Alice"); // Output Hello, Alice!

This design allows functions to adapt to more scenarios and reduces the chance of errors.

4. Where to put the function? Some practical suggestions

• Concentrate common functions into a file , such as functions.php , and then introduce them through include or require .
• Avoid repeatedly defining functions , otherwise an error will be reported. You can use function_exists() to check whether it is defined.
• Naming should be meaningful , for example, calculateTotalPrice() is clearer than calc() .

Basically that's it. Functions are one of the most basic and practical structures in programming. If you write too much, you will find that it makes the code cleaner and the logic clearer.

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