php执行代码，但它在屏幕上生成实际代码而不是我想要的结果。

Question

我提交了一个HTML表单旁边的代码，一旦提交表单，php文件应该执行它的任务，但它只打印出屏幕上的实际php代码。我不确定它是否是形式值，或者我只是错过了简单的错误，但任何帮助都会非常感激。

我提交了一个HTML表单旁边的代码，一旦提交表单，php文件应该执行它的任务，但它只打印出屏幕上的实际php代码。我不确定它是否是形式值，或者我只是错过了简单的错误，但任何帮助都会非常感激

<?php
//linking table to form
$studentid=$_POST["id"];

//To print out student ID
echo "You have selected Student ID: $studentid <br />";


//define what the file equals to which is the students ID
$file = "$studentid.txt";

//Opening the selected files
$fileopen = fopen($file,'r') or die("Sorry, cannot open $file");
if($fileopen){

while (($buffer=fgets($fileopen,4096))!==false){
//    echo $buffer."<br/>";
}    
if(!feof($fileopen)){
    echo "Error:unexpected fgets() fail\n";

}    
fclose($fileopen);    
}

//remove all commas from txt file
$filearray=file("$studentid.txt");
$count=count($filearray);

    for($i=0; $i<$count; $i++){

    $startnum=0;
    $stringlength = strlen($filearray[$i]);
    $comma = strpos($filearray[$i], ",", $startnum);
    $array[$i][0] = substr($filearray[$i], $startnum, $comma);
    $j=1;

        while ($j<$count-1){
            $comma = strpos($filearray[$i], ",", $startnum);
            $comma2 = strpos($filearray[$i], ",", $comma+1);
            $sub = $comma2-$comma;
            $num = substr($filearray[$i], $comma+1, $sub -1);
            $startnum = $comma2;
            $array[$i][$j]= $num;

        $j++;
        }
    $stop = $stringlength - $comma2;
    $array[$i][$j] = substr ($filearray[$i], $comma2 + 1, $stop);
    }

//table heading
 echo"<h1>The Original Table</h1>";

 //creating the rows and columns for the txt file
 echo "<table border = 1 >";
    for($row=0; $row<$count; $row++){
        print "<tr>";

    for($col=0; $col<$count; $col++){
        print "<td>".$array[$row][$col]."</td>";
    } 
}
echo "</table>";

// transpose function
function transpose_matrix($a, $c){
    //saving the new array
    $t_arr = array(); 
    //table heading
     echo"<h1>Transpose Matrix</h1>";

     //creating the rows and columns for the txt file
     echo "<table border = 1 >";
        for($row=0; $row<$c; $row++){
            print "<tr>";
               //saving the new array columns
$n_col=array();
        for($col=0; $col<$c; $col++){
            $t_arr[$col][$row] = $a[$col][$row];   //reversing the column and row to transpose the table

            print "<td>".$a[$col][$row]."</td>";
        } 

    }
    echo "</table>";
    return $t_arr;
}


$aa = transpose_matrix($array, $count);


echo "<h1>Sum Matrix</h1>";

function sum_matrix($arr, $co) {

     $t_arr = array();    
$s=0;   //Declaring the total
 echo "<table border = 1 >";
    for ($row=0; $row< $co; $row++) {  
        print "<tr>";
 for($col=0; $col<=$row; $col++) {  
     $s+= $arr[$col][$row];   //Adding the rows and columns in the new array
      print "<td>".$arr[$col][$row]."</td>";

} 
    } echo "</table>";

    return $s;   //returning the total
}


$b= sum_matrix($array, $count);   //assigning the result of the function into a new variable 

echo "<br />The total sum of the lower diagonal in the array is ".  $b;



 ?>