How do appending to associative array with variables work - php

Question

i'm doing this exercise to understand te concepts and syntax of php.The error i get is that the array is not being appended by a new entry from a text box, if i hard code the values the program works fine and prints the array values. but as soon as i put the variable it just assign a new value to the [0] index.
here is the code:
<label for="Name">Student Name:
<input type="text" name="StdName" placeholder="Your name">
</label>
<label for="Name">Grade:
<input type="text" name="StdGrade" placeholder="Your Grade">
</label>
<input type="submit" name="submit"value="submit">
</form>
<?php
// Associative array new
$studentName = $_POST['StdName'];
$studentGrade = $_POST['StdGrade'];
$classGrades = Array();
$classGrades['name'][] = $studentName;
$classGrades['grade'][] = $studentGrade;
echo "<br> <br> Your name is: $studentName and your grade is: $studentGrade <br> <br>";
foreach($classGrades as $key=>$value){
echo join($value,' <br>');
}
?>```

Answer 1

Your loop is wrong. You have separate name and grade arrays, so that's what you need to loop over:
foreach ($classGrades['name'] as $index => $name) {
$grade = $classGrades['name'][$index];
echo "$name<br>$grade<br>";
}
But it would be better if you didn't create separate array and kept the name and grade together in a single associative array:
$classGrades[] = ['name' => $studentName, 'grade' => $studentGrade];
Then your loop would look like:
foreach ($classGrades as $grade) {
echo $grade['name'] . "<br>" . $grade['grade'] . "<br>";
}
If you want the variable to persist between form submissions, you need to use a session variable.
Put
<?php
session_start();
at the beginning of the script. Then use $_SESSION['classGrades'] instead of $classGrades, and initialize it like this:
if (!isset($_SESSION['classGrades'])) {
$_SESSION['classGrades'] = array();
}

Answer 2

Basically you need to store your values, in some database.
Here is a simple start using a json file named students.json as database. That file will be created along your php file in the same folder, if not existing.
First you was missing the form elements and the method (by default it uses GET, thus this was not working).
Testing with isset() avoids populating the database with empty values, at page load or refreshs.
This is not very secure as such, you will have to work on that later on. Hint: What if a user insert a quote ' or " in his name?
<form method="post">
<label for="Name">Student Name:
<input type="text" name="StdName" placeholder="Your name">
</label>
<label for="Name">Grade:
<input type="text" name="StdGrade" placeholder="Your Grade">
</label>
<input type="submit" name="submit"value="submit">
</form>
<?php
if (!is_file("students.json")){
file_put_contents("students.json", json_encode([]) );
}
$classGrades = json_decode(file_get_contents("students.json"),true);
if (isset($_POST['StdName']) && isset($_POST['StdGrade'])){
var_dump($classGrades);
$studentName = $_POST['StdName'];
$studentGrade = $_POST['StdGrade'];
$classGrades['name'][] = $studentName;
$classGrades['grade'][] = $studentGrade;
echo "<br> <br> Your name is: $studentName and your grade is: $studentGrade <br> <br>";
file_put_contents("students.json",json_encode($classGrades));
}
echo "<table><tr><th>Name</th><th>Grade</th></tr>";
for ($i = 0;$i < count($classGrades['name']);$i++){
echo "<tr><td>".$classGrades['name'][$i] . "</td><td> " .$classGrades['grade'][$i] . "</td></tr>";
}
echo "</table>";