Quadratic equation solver in php

Question

I tried to make a quadratic equation solver in php:

index.html:

<html> <body> <form action="findx.php" method="post"> Find solution for ax^2 + bx + c<br> a: <input type="text" name="a"><br> b: <input type="text" name="b"><br> c: <input type="text" name="c"><br> <input type="submit" value="Find x!"> </form> </body> </html>

findx.php:

<?php if(isset($_POST['a'])){ $a = $_POST['a']; } if(isset($_POST['b'])){ $b = $_POST['b']; } if(isset($_POST['c'])){ $c = $_POST['c']; } $d = $b*$b - 4*$a*$c; echo $d; if($d < 0) { echo "The equation has no real solutions!"; } elseif($d = 0) { echo "x = "; echo (-$b / 2*$a); } else { echo "x1 = "; echo ((-$b + sqrt($d)) / (2*$a)); echo "<br>"; echo "x2 = "; echo ((-$b - sqrt($d)) / (2*$a)); } ?>

the problem is that it's returning wrong answers (d is right,x1 and x2 are not) seems like sqrt() is returning zero or maybe something else.

What results did you get for what input parameters? And what did you expect? — Ocaso Protal
– Ocaso Protal, Commented Apr 16, 2015 at 12:44

Chris Brendel · Accepted Answer · 2015-04-16 12:43:33Z

4

There's a typo in this line:

elseif($d = 0)

which is assigning the value 0 to $d instead of comparing it. That means you are always evaluating sqrt(0), which is 0, in your else block.

It should be:

elseif($d == 0)

answered Apr 16, 2015 at 12:43

Chris Brendel

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1 Comment

Richard Over a year ago

In languages where such assignments doesn't give at least a warning, a useful habit is to put the constant on the left: if (0 = $d) will fail.

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