Detailed explanation of php functions - study notes_PHP tutorial

Function is a commonly used and reasonable method in PHP that can be reused. Functions are divided into system functions and user-defined functions. Now I will introduce to you how to use these two PHP functions. Friends who need to know more Available for reference.

System function

Such as phpinfo(); this is a system function. We won’t say much about system functions. You can directly refer to the PHP tutorial or manual.

User-defined function

php introduces the concept of functions to make the program simpler and faster. A function is a program that implements a certain function. This program is equivalent to a module. It can be called and used with some simple commands when needed, without having to rewrite it every time. Just like a computer, we don't need to understand the complex structure inside, we only need to understand the functions it provides and use it directly.

php custom function-although php has many built-in practical functions, it is impossible to meet the needs of actual design. At this time, we need to create the function ourselves.

Basic structural form:

The code is as follows

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代码如下	复制代码
function 函数名(参数){  语句体 }

function function name (parameter){

Statement body

}

function is a declared function;

Function names must be unique. Unlike variable names, function names are not case-sensitive; There must be a space between function and function name;

Parameters can be omitted, or multiple parameters can be added, separated by commas.

PHP calls functions - after we define the function, we can call the function through the following structural form:

Function name (parameter)

代码如下	复制代码
function e(){ $i=5+6; echo $i; } e(); ?>

Parameters can be omitted, but the parentheses must be retained.

Example:

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function e(){ $i=5+6; echo $i; } e(); ?>

代码如下	复制代码
function sum($num,$price){ $total=$num*$price; echo "总价格为：$total"; } sum(10,78); ?>

Pass parameters of function

If the function defines parameters, then you must pay attention to the passing of parameter values ​​when calling the function. There are two ways to pass PHP function parameters: pass by value and pass by reference. The default is pass by value.

1. Pass by value:

Example 1:

代码如下	复制代码
function add($a,$b=10){ /* 定义变量$b默认参数 */ $sum=$a+$b; echo $sum ." ";  }  add(1,5);   /* 按值传递参数代替默认参数 */  add(1);    /* 没有给$b传递参数将采用默认值 */ ?>

The code is as follows	Copy code
function sum($num,$price){<🎜> $total=$num*$price;<🎜> echo "The total price is: $total";<🎜> }<🎜> sum(10,78);<🎜> ?>

Default parameters php function default parameters - If the value of the parameter is not provided when using a function, the parameter will use the default value specified by the function, and the default value must have been assigned when the function is defined. Example:

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function add($a,$b=10){ /* Define variable $b default parameters */<🎜> $sum=$a+$b;<🎜> echo $sum ." "; } add(1,5); /* Pass parameters by value instead of default parameters */ add(1); /* If no parameter is passed to $b, the default value will be used */ ?>

Function return value

When we design a program, many times we don’t want the results of the function to be displayed directly in the browser. In this case, we can use the return statement to call the function value first and then perform other operations.

php function return value example:

The code is as follows

代码如下	复制代码
function add($a,$b=10){ $sum=$a+$b; return $sum; /* 将$sum的值赋给函数 */ } $sum=add(1,5); /* 这里变量$sum得到函数的值 */ echo $sum ." "; ?>

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function add($a,$b=10){
$sum=$a+$b;
return $sum; /* Assign the value of $sum to the function */
}
$sum=add(1,5); /* Here the variable $sum gets the value of the function */
echo $sum ."
";
?>

Function Nested Call

代码如下	复制代码
function volume($l,$w){ function height($a){ $a=$a/2; return $a; } $a=$l*$w; $v=$a*height($a); echo $v; } volume(8,3); ?>

The inside of a function can not only be a general execution statement, but also a function. This is how PHP function nesting is used. Function nesting: Only one function also calls other functions. What should be understood here is that each function is in a parallel relationship, and the definition of the function is independent. Just like a container can contain many small containers, and these containers are independent of each other and each contain their own things.

Example:

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function volume($l,$w){
function height($a){
$a=$a/2;
Return $a;
}
$a=$l*$w;
$v=$a*height($a);
echo $v;
}
volume(8,3);
?>

代码如下	复制代码
function calculate($n){ if($n==0) return 1; else return $n*calculate($n-1); } $s=calculate(3); echo $s; ?>

Function recursive call

What is php recursive function? Before explaining this concept, let's look at a mathematical example. If you want to calculate the factorial of n, that is, n!, you should first know (n-1)!, and to know (n-1)!, you must know (n-2)!. By analogy, until 1!=1, and then return to calculate 2!,3!...(n-1)!,n!, you can finally get the result of n factorial. The meaning of recursive calling of PHP function is that the function can call itself. This direct or brief operation of calling the function itself is allowed in the PHP language and becomes a recursive function. Example:

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function calculate($n){ if($n==0) Return 1; else return $n*calculate($n-1); } $s=calculate(3); echo $s; ?> http://www.bkjia.com/PHPjc/628827.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/628827.htmlTechArticleIn PHP, functions are a common and reasonable method that can be reused. Functions are system functions and user-defined functions. Define functions, let me introduce to you how to use these two php functions...