How to play with PHP custom functions (summary sharing)

In the previous article, I brought you "How to use the For loop and Foreach loop in PHP (detailed picture and text explanation)". This article introduces in detail how to use and To distinguish between PHP's for loop and foreach loop, this article will take a look at the custom functions in the basic syntax of PHP functions. Hope it helps everyone!

PHP custom functions

PHP has provided us with many powerful system functions, but this is far from meeting the needs of programmers. A custom function can be created according to development needs. Functions are executed by calling functions. An example of the basic syntax format of a custom function is as follows:

function 函数名 (参数1, 参数2, ..., 参数n){
    函数中的功能体;
    return 返回值;
}

The above syntax format has the following characteristics:

• The first line of each function is composed of three parts: the keyword declaring the function function, the function name and the parameter list;

• Every custom function must start with function, that is, use function declaration;

• Function can have return value or no return value;

• A function cannot be defined twice, that is, the function cannot be overloaded;

• When declaring a function, the parentheses "()" after the function name are also required. The parentheses contain a set of parameter lists. The parameters are the declared variables, and then the variables can be passed to the function when the function is called. The parameter list can be empty or have one or more parameters. Use commas to separate multiple parameters;

• After the function is created, it will Likewise, you can call functions anywhere on the page.

<?php
function a(){
   echo &#39;这是一个函数示例&#39;;
}
a();
a();
a();
?>

Output result:

• Function name and variables The naming rules are the same, but the difference is: function names are not case-sensitive .

<?php
function ABC(){
   echo &#39;函数名不区分大小写<br />&#39;;
}
aBC();
AbC();
ABc();
?>

Output result:

• The function is still defined before it is defined It can be called later. That is, the function can be called anywhere.

<?php
a();
function a(){
   $b = &#39;好好学习&#39;;
   $b .= &#39;天天向上&#39;;
   echo $b;
}
a();
?>

Output result:

• Function action execution module If there is a return, the code after the return will not be executed.

<?php
function a(){
   echo "好好学习";
   return;
   echo "天天向上";
}
a();
?>

Output result:

• After the function execution is completed ,return can bring the value inside the function body out of the function body.

<?php
function a(){
   $b = 1;
   $c = 9;
   $d =  $b + $c;
   //将$d的结果进行返回
   return $d;
}
//调用a()这个函数，$b和$c相加的$d就会返回回来给到变量$e
$e = a();
//输出$e的结果
echo $e;
?>

Output result:

• Variables in the function body and outside the function body The variables have no relationship

<?php
//先在函数体前定义变量$a的值为10
$a = 10;
function demo( $a ){
   //形参带入了函数体内，函数体内变量$a 改为了 50
   $a = 50;
   echo $a + $a;
}
//将函数体外的变量$a，传入变量的参数处（实际传入的参数，实参），显示出的结果为100
demo($a);
//此处$hello的值输出，依然为10
echo $a;
?>

Output result:

• The function cannot be overloaded

<?php
function a(){
}
function a(){
}
?>

The output result will report an error, and the function cannot be overloaded.

Recommended learning: "PHP Video Tutorial"

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