How to display answer to a form? - php

Question

If im trying to post the answer on the same page would it look something like this? Not too sure whether I have used the correct functions, please check my code:
<form method="post" action="activity.php">
<input type="text" name= "num1" value="Enter a number"/>
<select name= "conversion">
<option>Select a conversion</option>
<option name="lb to kg">lbs to kgs</option>
<option name="kgs to lbs">kgs to lbs</option>
<option name="cm to in">cms to inchs</option>
<option name="inchs to cms">inchs to cms</option>
<option name="pints to litres">pints to litres</option>
<option name="litres to pints">litres to pints</option>
<option name="faranheit to centigrade">faranheit to centigrade</option>
<option name="centigrade ti faranheit">centigrade to faranheit</option>
</select>
<input type="submit" value="convert" />
</form>
Then the php after the form:
$num1 = $_GET["num1"];
$conversion = $_POST["conversion"];
if($conversion == "lbs to kgs")
{
$answer_lb = $num1 * 0.45;
echo $answer_lb;
}
if($conversion == "kgs to lbs")
{
$answer_kg = $num1 * 2.2;
echo $answer_kg;
}
if($conversion == "cms to inchs")
{
$answer_inch = $num1 * 2.54;
echo $answer_inch;
}
if($conversion == "inchs to cms")
{
$answer_cm = $num1 * 0.393;
echo $answer_cm;
}
if($conversion == "pints to litres")
{
$answer_pints = $num1 * 0.568;
echo $answer_pints;
}
if($conversion == "litres to pints")
{
$answer_litres = $num1 * 1.579;
echo $answer_litres;
}
if($conversion == "faranheit to centigrade")
{
$answer_faranheit = ($num1 - 32) * (5/9);
echo $answer_faranheit;
}
if($conversion == "centigrade to faranheit")
{
$answer_centigrade = ($num1 * 9/5) + 32;
}
?>
<em>
I wasnt sure whether or not the php code has to come before or after the form and was unsure about the form action.

Answer 1

//EDITED the answer according to your needs:
Here's a working example of the code below: http://codepad.viper-7.com/vu6j0N
<?php
$calculation_models = array();
$calculation_models[] = array('description'=>'lb to kg',
'calculation' => function($val) { return $val * 0.45; }
);
$calculation_models[] = array('description'=>'kgs to lbs',
'calculation' => function($val) { return $val * 2.2; }
);
$calculation_models[] = array('description'=>'cm to in',
'calculation' => function($val) { return $val * 2.54; }
);
$calculation_models[] = array('description'=>'inchs to cms',
'calculation' => function($val) { return $val * 0.393; }
);
$calculation_models[] = array('description'=>'pints to litres',
'calculation' => function($val) { return $val * 0.568; }
);
$calculation_models[] = array('description'=>'litres to pints',
'calculation' => function($val) { return $val * 1.579; }
);
$calculation_models[] = array('description'=>'faranheit to centigrade',
'calculation' => function($val) { return ($val - 32) * (5/9); }
);
$calculation_models[] = array('description'=>'centigrade to faranheit',
'calculation' => function($val) { return ($val * 9/5) + 32; }
);
if (isset($_GET['val']) && isset($_GET['model'])) {
$result = $calculation_models[$_GET['model']]['calculation']($_GET['val']);
echo 'The result is ' . $result;
}
?>
<!-- build the form dynamically from the array above -->
<form method="get" action="#">
<input type="text" name="val" placeholder="Enter a number"/>
<select name="model">
<?php foreach($calculation_models as $key => $model) : ?>
<option value="<?php echo $key; ?>"><?php echo $model['description']; ?></option>
<?php endforeach; ?>
</select>
<input type="submit" value="convert" />
</form>

Answer 2

if you are asking this question, then it is not exactly simple. To change the content of the page without reloading a new page usually involves a technique known as AJAX,
basically, it uses javascript to submit the request, and javascript will again process the response after it is received.

Answer 3

I assume you have to files like: calculator.html and calculator.php
calculator.html is the form.
The first solution to make the result display on the same page is simple:
put everything into caclculator.php like this
<?php
if($_GET["submit"]){
#your code
}
?>
<html>
<!-- your html -->
</html>
If this was not what you asked for, the next method is using an iframe "with the result" and javascript to send your data to the iframe.
And the last solution is plain-ajax.