Three elements of php function

Declare and apply various forms of PHP functions (Recommended learning: PHP video tutorial)

Whether we are using a system function or a custom function, we must understand a function through the following three elements of the function:

function description, function The parameters and the return value of the function.

Function of regular parameters

Function format description of regular parameters:

string example(string name,int age,double height)

The so-called function of regular parameters is the sum of actual parameters and The formal parameters should be equal in number and consistent in type. Just like strongly typed languages ​​like C or Java.
The above function has three parameters. The number and order of parameters passed when calling must be consistent.

string chr(int $ascii)   //返回指定的字符
float ceil(float $value) //进一法取整
array array_combine(array $keys,array $values)//合并一个数组
string implode(string $glue,array $pieces)

Function of pseudo-type parameters

Function format description of pseudo-type parameters:

mixed funName(mixed $a, number $b, callback $c)

PHP is a weakly typed language, not only when declaring variables There is no need to specify a type, and of course there is no need to specify a type when declaring a function, so in PHP, any type of value can be passed to each parameter of the function.

Three pseudo-types: mixed, number and callback.

bool empty(mixed $var)    //检查一个变量是否为空
bool usort(array &$array,callback $cmp_function)
//使用用户自定义的比较函数对数组中的值进行排序
number abs(mixed $number)  //绝对值

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