Detailed explanation of parameter examples of PHP custom functions

The parameter list consists of 0, one or more parameters. Each argument is an expression, separated by commas. For functions with parameters, there is a data transfer relationship between the called functions in the PHP script program. The previous chapter explained How to call PHP custom functions, This chapter will explain PHP custom functions with examples. Define parameter usage in functions. When we define a function, the expression in parentheses after the function name is called a formal parameter, abbreviated as " formal parameter"; the expression in parentheses after the called function name is called an actual parameter, abbreviated as "Actual parameters", the actual parameters and formal parameters need to correspond to the passed data in order.

If the function does not have a parameter list, the task performed by the function is fixed, and the user cannot change some execution behaviors inside the function when calling the function. For example, given a table() function without a parameter list, a fixed table will be output every time the table() function is called. The user cannot even change the basic table name, the number of rows and columns of the table.

If the function uses a parameter list, the specific values ​​of the function parameters will be obtained from outside the function. That is, when the user calls the function, some data will be passed to the function through the parameter list before the function body is executed. Inside the function, when the function executes the function body, it can decide how to execute the function body based on the data passed by the user. Therefore, the parameter list of a function is the operation interface provided to the user when calling the function. We can give a table() function and add three parameters to the function parameter list, so that the user can change the table name, number of rows, and number of columns of the table when calling the table() function. The code is shown as follows:

<?php
 /*
  * 声明三个参数，参数之间用逗号隔开
  * $table_name  字符串类型的表名
  * $rows        整型的表格行数
  * $cols        整型的表格列数
  */
 function table($table_name, $rows, $cols){
   echo "<table align=&#39;center&#39; border=&#39;1&#39; width=&#39;600&#39;>";
   echo "<caption><h2>$table_name</h2></caption>";
   for($i=0; $i<$rows; $i++){
     $color = $i%2 == 0?"#ffffff":"#dddddd";
     echo "<tr bgcolor=&#39;.$color.&#39;>";
     for($j=0; $j<$cols; $j++){
       echo "<td>".($i*$cols+$j)."</td>";
     }
     echo "</tr>";
   }
   echo "</table>";
 }
?>

When defining the function table(), three formal parameters are added: the first parameter requires a string type table name; the second string is the row of the table. The number requires an integer value; the third parameter is the number of columns in the output table, which is also an integer value. These three formal parameters are used in the form of variables in the function body. They are assigned values ​​when the user calls them and are used during the execution of the function body.

The parameter list used in the function allows the user to pass data to the internal interface of the function when calling the function. You can set as many parameters as needed when declaring the function. For example, users can call the table() function to change the width, background color, table border width, etc. of the table. Just set a few more parameters in the parameter list when declaring the function.

This chapter introduces the parameters of PHP custom functions. The expressions in parentheses after the function name are called formal parameters; the expressions in parentheses after the called function name are called actual parameters. In the next chapter, I will introduce to friends several ways in which parameters of php custom functions can be passed between functions.

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