PHP计算器，具有4个可更改的选项

Question

嘿，我已经建立了这个小计算器，并认为我会分享它，以便对更多人有所帮助:) 您只需要更改$ opt变量的值即可获得不同的输出。 如果您有任何意见或改进，请随时添加。 当我有空的时候，我会发布更多。

<?php
$opt = "Example 1";

$x;
$x1;

switch ($opt) {
      case "Example 1": 
           $keywords = array("add", "multiply", "apply");
           $values = array("2", "3", "4");
           break;
      case "Example 2":
           $keywords = array("multiply", "apply");
           $values = array("9", "5");
           break;
      case "Example 3":
           $keywords = array("apply");
           $values = array("1");
           break;
      case "Example 4":
           $keywords = array("divide", "substract", "apply");
           $values = array("2", "3", "8");
           break;
      default:
           echo "No valid example has been chosen";
           break;
}

$klen = count($keywords);
$klen -=1;
$x = $values[$klen];
echo "Apply " .$x. "\n";

$klen -=1;
$j =0;

foreach ($keywords as $i) {
   $x1 = $values[$j];
   $j +=1; 

    switch ($i) {
      case "add": 
           $x += $x1;
           echo "Add " .$x1. "\n";
           break;
      case "multiply":
           $x *= $x1;
           echo "Multiply " .$x1. "\n";
           break;
      case "divide":
           $x /=$x1;
           echo "Divide " .$x1. "\n";
           break;
      case "substract":
           $x -=$x1;
           echo "Substract " .$x1. "\n";
           break;
      case "apply":
           break;      
    }
}

    echo "The result is " .$x;    

?>