You must understand the parameters of the function (in detail)

The last article introduced you to "Let’s talk about the difference between the return statement and echo (detailed explanation and examples)". This article continues to introduce the parameters of the function to you. Now let’s go and take a look. Look! ! !

Parameters of function (actual parameters and formal parameters):

Formal parameter variables only allocate memory units when called , at the end of the call, the allocated memory unit is released immediately. Therefore, formal parameters are only valid within the function. After the function call ends and returns to the calling function, the formal parameter variable can no longer be used.

Actual parameters can be constants, variables, expressions, functions, etc. No matter what type of quantities the actual parameters are, they must have definite values ​​when making function calls so that these values ​​can be transferred to formal parameters. Therefore, assignment, input, etc. should be used in advance to obtain a certain value for the actual parameters.

The actual parameters and formal parameters should be strictly consistent in number, type, and order, otherwise a "type mismatch" error will occur.

The data transfer that occurs in function calls is one-way. That is, only the value of the actual parameter can be transferred to the formal parameter, but the value of the formal parameter cannot be transferred in the reverse direction to the actual parameter. Therefore, during the function call, the value of the formal parameter changes, but the value of the actual parameter does not change.

Simply put, parameters are divided into two parts: formal parameters and actual parameters:

Formal parameters are formal parameters, used in parentheses when defining functions;

The actual parameter is the actual parameter, used in the parentheses of the calling function;

For example, int F(int i) i is the formal parameter,
The actual parameter is the function call When there are parameters passed by the calling function to the called function, for example:

int x=1;
a=F(x);

x here is the actual parameter. After the function is called, the value of x is passed to the formal parameter. i

Note:

• If the function has defined parameters, the corresponding actual parameters must be passed in when calling the function (When the formal parameter has no default value)

• If the function also has the default value of the formal parameter and the corresponding actual parameter is passed in, then the passed actual parameter will be the main one (equivalent to For variable assignment, use the value of the actual parameter to assign the value to the formal parameter)

The specific operation takes the code as an example:

<?php
     /******函数的参数 */
     function table (){
         $str = &#39;<table border="1" align="center" width="800">&#39;;
         for ($tr = 0; $tr < 10; $tr ++){
             $str .= &#39;<tr>&#39;;
             for($td = 0; $td < 10; $td ++){
                $str .= &#39;<td>&#39;.$tr.$td. &#39;</td>&#39;;
            }
            $str .= &#39;</tr>&#39;;
         }
         $str .= &#39;</table>&#39;;
         //返回值  返回一个表格
         return $str;
     }
     $table = table();
     echo $table;
?>

The demonstration results are as follows:

Code analysis:

We use the function function to define a table, and then set the specifications of the table (supplementary: align refers to adjustment, calibration, center: center), and then set Define the for loop, enter the for loop and continue to set the second for loop statement. The specific code is as shown above. At the end, we use return to return the value (the purpose is to determine whether the return statement can return a value successfully and whether it can return a table. ), when we return a table, call the table statement, {$table=table()}, output (table). Overall, we first define a variable (table), connect one (tr tag) in the table, and then connect 10 (td). At this time, the loop ends, and we connect an end flag (/td). At this time, we continue Loop, and so on;

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