How do I get a table to print only certain information from a file?

I’m going to apologize in advance. This is probably a very stupid question, but I can’t figure it out. What I’m trying to do is to use a radio button selection to look through a file and print out the things that align with the radio selection. Unfortunately, all it does is print the entire thing at once. How do I fix this?

<section id="leftcol">
    <h1> Select Grade to List:</h1>
    <form action="hwk9.php" method="post">
    <input type="radio" name="l_grade" value="A"> A <br />
    <input type="radio" name="l_grade" value="B"> B <br />
    <input type="radio" name="l_grade" value="C"> C <br />
    <input type="radio" name="l_grade" value="D"> D <br />
    <input type="radio" name="l_grade" value="F"> F <br />
    <input type="submit" name="submit" value="Submit">
    </form>
</section>

<section id="rightcol">
    <?
        $submit=$_POST['submit'];
        if (isset($submit)) {
            $l_grades=$_POST['l_grade'];
            $names=file("student.names.txt");
            $grades=file("student.grades.txt");
            $names=explode(PHP_EOL, $names);
            $grades=explode(PHP_EOL, $grades);
            print "<table>
            <th> Name </th>
            <th> Grade </th>";
            $i = 1;
            if ($l_grades="A" and $grades >= '90') {
                foreach ($names as $i=>$name) {
                    print "<tr> 
                    <td> $names </td>
                    <td> $grades </td>
                    </tr>";
                }
            }

I only included one of the smaller conditionals because they all look the same, seeing as I copy/pasted them and only changed the bits that needed to be changed.

Answer

You are on the right track. You just missed on = sign between $l_grades and “A”. Since it is $l_grades=”A” it is assigning the value “A” to $l_grades so it is always true. Try using:

if ($l_grades=="A" and $grades >= '90') {
            foreach ($names as $i=>$name) {
                print "<tr> 
                <td> $names </td>
                <td> $grades </td>
                </tr>";
            }
        }