What is the difference between formal parameters and actual parameters of a PHP function?

In PHP functions, formal parameters are placeholders when the function is defined, representing the data to be received, and actual parameters are the actual data passed to the formal parameters when the function is called. Formal parameters can specify types and default values, and actual parameters can be passed positionally or by name.

Formal parameters and actual parameters of PHP functions: in-depth understanding

Formal parameters and actual parameters

In PHP functions, formal parameters (parameters) are placeholders specified when defining the function and are used to receive the data actually passed to the function. Argument is the data passed to the formal parameter when the function is actually called.

Types and default values ​​of formal parameters

Formal parameters can specify a type (such as integer, string) or a default value. If no default value is specified, the variable's type is mixed, which means it can receive any type of data. For example:

function add($num1, $num2 = 0) {
  // ...
}

Passing actual parameters

Parameters can be passed to functions by position or by name:

• By position Passing: The actual parameters are in the same order as the formal parameters.
• Pass by name: Use formal parameter names as keys and pass actual parameters as values.

For example:

$result = add(10, 20); // 按位置传递
$result = add(num2: 20, num1: 10); // 按名称传递

Practical case: Calculate the area of ​​a circle

<?php
function calculateAreaCircle($radius) {
  return pi() * $radius ** 2;
}

$radius = 5;
$area = calculateAreaCircle($radius);

echo "圆的面积为：$area";
?>

Summary

• Formal parameters are used to define placeholders for data received by the function, and actual parameters are the data actually passed to the function.
• Formal parameters can specify types and default values.
• Actual parameters can be passed positionally or by name.

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