Basic tutorial on PHP custom function declaration, calling, parameters and return values

Like functions in mathematics, y=f(x) is the basic expression form of the function, x can be seen as parameters, y can be seen Doing returns a value, that is, a function definition is a named, independent piece of code that performs a specific task and may return a value to the program that calls it.

Custom function

Declaration of function

In the process of writing programs, we often encounter certain functional modules that are not available in PHP To provide system functions, we need to define the function ourselves, that is, a custom function. The rules for custom functions are as follows:

• The first line of each function is the function header, consisting of Declaring a function consists of three parts: keyword function, function name and parameter list.

• Each custom function must be declared using the function keyword.

• The function name can represent the entire function, and the function can be named any name, as long as it follows the naming rules of variable names. However, the function name must be unique and cannot have the same name as the system function.

• When declaring a function, the curly braces after the function name are also required. The curly braces indicate a set of acceptable parameter lists. The parameters are the declared variables, and then the function is called. value is passed to it. The parameter list can have none, one or more parameters, and multiple parameters are separated by commas.

• The function body is located after the function header and enclosed in curly braces. After the function is called, execution ends after the retun statement or the outermost curly brace, and returns to the calling program.

• Use the keyword return to return a value from the function and then return to the calling program to continue execution.

Demo

<?php 
    /* 将使用双层for循环输出表格的代码声明为函数，函数名为table */
    function table() {                              
        echo "<table align=&#39;center&#39; border=&#39;1&#39; width=&#39;600&#39;>";           
        for($out=0; $out < 10; $out++ ) {       
            $bgcolor = $out%2 == 0 ? "red" : "blue";//各行换背景色            
            echo "<tr bgcolor=".$bgcolor.">"; 
            for($in=0; $in <10; $in++) {    
                echo "<td>".($out*10+$in)."</td>";    
            }            echo "</tr>";    
        }        echo "</table>";
    } 
?>

Call of function

Whether it is a custom function or a system function, if the function is not called, it will not be executed. After the function is called, it starts executing the code in the function body. After the execution is completed, it returns to the calling location and continues downward execution. The calling rules are as follows:

• Call the function through the function name.

• If the function has a parameter list, you can also pass the corresponding value to the parameter through the parentheses after the function name, and use the parameters in the function body to change the execution behavior of the code inside the function.

• If the function has a return value, when the function is executed, the value following return will be returned to the location where the function was called.

Demo

<?php 
    /* 将使用双层for循环输出表格的代码声明为函数，函数名为table */
    function table() {                              
        echo "<table align=&#39;center&#39; border=&#39;1&#39; width=&#39;600&#39;>";           
        for($out=0; $out < 10; $out++ ) {       
            $bgcolor = $out%2 == 0 ? "red" : "blue";//各行换背景色            
            echo "<tr bgcolor=".$bgcolor.">"; 
            for($in=0; $in <10; $in++) {    
                echo "<td>".($out*10+$in)."</td>";    
            }            echo "</tr>";    
        }        echo "</table>";
    } 
?>  

Parameters of the function

The parameter list is composed of zero, one or more parameters. Each argument is an expression, separated by commas. For parameterized functions, there is a data transfer relationship between the PHP script program and the called function. When defining a function, the expressions in parentheses after the function name are called formal parameters (referred to as "formal parameters"), and the expressions in parentheses after the called function name are called actual parameters (referred to as "actual parameters"). Actual parameters and formal parameters Data needs to be transferred in sequence. If the function does not have a parameter list, the tasks performed by the function are fixed, and the user cannot change some of the internal execution behaviors of the function when calling the function.

Demo

<?php 
    /**自定义函数table()时，声明三个参数，参数之间使用逗号分隔        
    @param  string  $tableName  需要一个字符串类型的表名        
    @param  int     $rows       需要一个整型数值设置表格的行数        
    @param  int     $cols       需要另一个整型值设置表格的列数    */
    function table( $tableName, $rows, $cols ) {                    
        echo "<table align=&#39;center&#39; border=&#39;1&#39; width=&#39;600&#39;>";       
        echo "<caption><h1 id="nbsp-tableName-nbsp"> $tableName </h1></caption>";            
    
        for($out=0; $out < $rows; $out++ ) {    //使用第二个参数$rows指定表行数
            $bgcolor = $out%2 == 0 ? "red" : "blue";            
            echo "<tr bgcolor=".$bgcolor.">"; 

            for($in=0; $in < $cols; $in++) {    //使用第三个参数$cols指定表列数
                echo "<td>".($out*$cols+$in)."</td>";    
            }            echo "</tr>";    
        }        echo "</table>";
    } 
?>  
<?php 
table("表格",10,10);
?>

The return value of the function

The return value of the function is the result of function execution. The script program that calls the function cannot directly Use the information in the function body, but you can pass data to the caller through the keyword return. Notes on the return statement are as follows: The

• return statement can return any execution result value in the function body to the function caller.

• If the return statement is executed in the function body, the statements following it will not be executed.

Demo

<?php 
    /**        自定义函数table()时，声明三个参数，参数之间使用逗号分隔        
    @param  string  $tableName  需要一个字符串类型的表名        
    @param  int     $rows       需要一个整型数值设置表格的行数        
    @param  int     $cols       需要另一个整型值设置表格的列数    */
    function table( $tableName, $rows, $cols ) {        $returnStr="这是返回的字符串";
        echo "<table align=&#39;center&#39; border=&#39;1&#39; width=&#39;600&#39;>";       
        echo "<caption><h1 id="nbsp-tableName-nbsp"> $tableName </h1></caption>";            
    
        for($out=0; $out < $rows; $out++ ) {    //使用第二个参数$rows指定表行数
            $bgcolor = $out%2 == 0 ? "red" : "blue";            
            echo "<tr bgcolor=".$bgcolor.">"; 

            for($in=0; $in < $cols; $in++) {    //使用第三个参数$cols指定表列数
                echo "<td>".($out*$cols+$in)."</td>";    
            }            echo "</tr>";    
        }        echo "</table>";
        return $returnStr;
    } 
?>  
<?php 
echo table("表格",10,10);
?>

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