PHP tutorial: PHP custom function application

Definition of function: A function is an encapsulated block of code that can be called at any time. There are two types of functions in PHP: Custom functions and system functions.

Custom function syntax format:

function function name ([parameter 1, [parameter 2]....])

{

function Body (program content description)

[return return value;]

}

Note: The things in [] are optional

Customized The name of the function:

1. It is the identification name of the function in the program code. The function name can be any character starting with a letter or underscore followed by zero or more letters, underscores and numbers. string.

2. Conform to the naming rules of variable names

3. Function names are not case-sensitive.

4. The function name cannot be repeated, and the declared function cannot be used when naming the function (this is different from the naming of variables, variables can overwrite the previous variable name, but functions cannot), and PHP system functionName.

The difference between function names and variable names:

Variable names are strictly case-sensitive, while function names are not case-sensitive.

Parameters (can be divided into formal parameters and actual parameters):

The so-called parameters are: used to pass values ​​from outside the function into the function body and used for calculation and processing.

The parameters are separated by ",". When the function does not require any values ​​to be passed in, the parameters can be omitted.

Formal parameters: When declaring a function, the expression in parentheses after the function name is called a formal parameter.

function table (formal parameter 1, formal parameter 2) {}

Actual parameters: The expression in parentheses after the called function name is called an actual parameter.

table (actual parameter 1, actual parameter 2);

The actual parameters and formal parameters need to pass data in order.

function table2($rows,$cols,$color='yellow')
{
    echo &#39;<table border="1" bgcolor="&#39;.$color.&#39;">&#39;;
    for($i = 0;$i < $rows;$i++){
        echo &#39;<tr>&#39;;
        for($n = 0;$n <$cols;$n++){
            echo &#39;<td>&#39;.($i*$rows+$n).&#39;</td>&#39;;
        }
        echo &#39;</tr>&#39;;
    }
}
table2(10,10,&#39;red&#39;);

Note: Among function parameters, those without default values ​​are placed at the front, and those with default values ​​are placed at the back of the parameter list.

table2($rows,$cols,$color = 'yellow')

Return value:

When calling a function and you need it to return some values, then you need to This is implemented using the return statement in the function body.

The format is as follows:

return return value; //The return value can be a variable or an expression

exit(); //No return value void

The return statement has the following two functions when used in the function body:

1. The return statement can return any value determined in the function body to the function caller.

2. Return program control to the caller's scope, that is, exit the function. If a return statement is executed in a function, the statements following it will not be executed.

Explanation: If the function does not return a value, it can only be regarded as an execution process. It is not enough to just rely on the function to do something. Sometimes it is necessary to do something in the program script

Use the result after function execution. Due to the difference in the scope of variables, the script program calling the function cannot directly use the information in the function body, but can pass data to the caller through the keyword return.

<?php
header("content-type:text/html;charset=utf-8");
echo show();
echo &#39;<hr>&#39;;

function show()
{
    echo &#39;ccc&#39;;
    return &#39;aaa&#39;;
    //return所在行之后的代码不会执行
    echo 111;
}

//函数的调用，不会将return后面的值返回
show();
echo &#39;<hr>&#39;;

//return返回的值 需要一个变量来接收它
$result = show();
echo $result;
echo &#39;<hr>&#39;;

//也可以直接输出 函数名称
echo show();
echo &#39;<hr>&#39;;

1. Whether it is a custom function or a system function, if the function is not called, it will not be executed.

2. Call the function through the function name and let the code of the function body run. The function body will be executed several times after calling it several times.

3. In PHP, you can call the function after the declaration of the function, you can also call it before the declaration of the function, and you can also call the function within the function.

function showInfo()
{
}
function ShowInfo()
{
}

Judge whether the function exists: function_exists()

if(function_exists('table')){
    echo 'table';
}else{
    echo 'table函数不存在，请先定义table函数';
}

Range of variables:

• 局部变量

• 全局变量

• 静态变量

<?php
$username = &#39;shifang&#39;;
function stu()
{
    $name = &#39;libai&#39;;
    echo $name;
    //无法调用外部的$username,而在函数体内也没有声明$username
10   echo $username;
    echo &#39;xxxx&#39;;
}

stu();
//函数体外无法调用函数体内的变量
16.echo $name;
echo $username;

结果：

libai

Notice: Undefined variable: username in D:\xampp\htdocs\89\Exercise\2016-7-28 PHP function\007quanju.php on line 10

xxxx

Notice: Undefined variable: name in D:\xampp\htdocs\89\Exercise\2016-7-28 PHP function\007quanju.php on line 16

shifang

在PHP的页面中声明的变量，叫“全局变量”.

函数内的变量叫“局部变量”.

二者没有半毛钱关系：函数内的变量，外部无法调用，函数外的变量，函数无法调用

（某戏班子到某学校唱戏，两者的花名册都不可相互调用）

静态变量：

• PHP支持声明函数变量为静态的(static)。

• 一个静态变量在所有对该函数的调用之间共享，并且仅在脚本的执行期间函数第一次被调用时被初始化。

• 要声明函数变量为静态的用关键字static,通常，静态变量的第一次使用时赋予一个初始值。

<?php
function tongji()
{
    static $n = 0;
    echo $n;
    $n++;
}
tongji();
tongji();
tongji();
echo &#39;<hr>&#39;;

function jishu()
{
    $m = 0;
    echo $m;
    $m++;
}
jishu();
jishu();
jishu();

输出结果：
0123

00000

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