Using PHP to code a simple calculator

Question

I'm creating a simple BMR calculator that calculates the following formula: BMR = 66 + ( 6.23 x weight in pounds ) + ( 12.7 x height in inches ) - ( 6.8 x age in year ). This code has been borrowed and modified so I'm not completely comfortable with it.

Im curious to as why the '66' is already displayed in answer before I press submit. How can I change my code to not display any values in the answer box until submit is pressed?

The calculator can be found here: http://rgoo.co/calculators/bmr-calculator.php

<?php
if (isset($_POST['agev'])) $agev = $_POST['agev'];
if (isset($_POST['feetv'])) $feetv = $_POST['feetv'];
if (isset($_POST['inchesv'])) $inchesv = $_POST['inchesv'];
if (isset($_POST['weightv'])) $weightv = $_POST['weightv'];

$totalheightv = $inchesv + ($feetv*12);
$answer = 66 + (6.23*$weightv) + (12.7*$totalheightv) - (6.8*$agev);
echo <<<_END
<form method='post' action='/calculators/bmr-calculator.php'>
<table border='0' width='500px' cellpadding='2' cellspacing='1' class="table">
<tr class="calcheading"><td colspan="2"><strong>IIFYM test</strong></td></tr>
<tr class="calcrow"><td>AGE:</td><td align="center"><input type='text' name='agev' value="$agev"/>Years</td></tr>
<tr class="calcrow2"><td>Height:</td><td align="center"><input type='text' name='feetv' value="$feetv"/>Ft</td></tr><td align="center"><input type='text' name='inchesv' value="$inchesv"/>In</td></tr>
<tr class="calcrow"><td>Weight:</td><td align="center"><input type='text' name='valuec' value="$valuec"/>lbs</td></tr>
<tr class="submit"><td colspan="2"><input type='submit' value='Calculate'/></td></tr>
_END;
?>

<tr class="calcrow">
<td>Your BMR is:</td>
<td align="center"><input type="text" value="<?php echo round($answer)?>"></td>
</tr>
</table>
</form>

nietonfir · Accepted Answer · 2013-12-27 09:50:45Z

3

Default to an empty value for your answer and only calculate when you have all your values:

<!doctype html>
<?php
$answer = "";
$agev = "";
$feetv = "";
$inchesv = "";
$weightv = "";

if (isset($_POST['agev']) && isset($_POST['feetv']) && isset($_POST['inchesv']) && isset($_POST['weightv'])) {
    $agev = $_POST['agev'];
    $feetv = $_POST['feetv'];
    $inchesv = $_POST['inchesv'];
    $weightv = $_POST['weightv'];

    $totalheightv = $inchesv + ($feetv*12);
    $answer = 66 + (6.23*$weightv) + (12.7*$totalheightv) - (6.8*$agev);

}

echo <<<_END
<form method='post' action=''>
<table border='0' width='500px' cellpadding='2' cellspacing='1' class="table">
<tr class="calcheading"><td colspan="2"><strong>IIFYM test</strong></td></tr>
<tr class="calcrow"><td>AGE:</td><td align="center"><input type='text' name='agev' value="$agev"/>Years</td></tr>
<tr class="calcrow2"><td>Height:</td><td align="center"><input type='text' name='feetv' value="$feetv"/>Ft</td></tr><td align="center"><input type='text' name='inchesv' value="$inchesv"/>In</td></tr>
<tr class="calcrow"><td>Weight:</td><td align="center"><input type='text' name='weightv' value="$weightv"/>lbs</td></tr>
<tr class="submit"><td colspan="2"><input type='submit' value='Calculate'/></td></tr>
_END;
?>

<tr class="calcrow">
<td>Your BMR is:</td>
<td align="center"><input type="text" value="<?php echo round($answer)?>"></td>
</tr>
</table>
</form>

This way you ensure that

the answer field is empty if nothing was submitted
all required values are available to ensure that the BMR is calculated properly
you get no PHP warnings for using undefined variables

And I fixed a small issue you had in your version of the code, where you used the name valuec for the weight input field as opposed to weightv in your code. And please add any missing HTML tags (like the doctype, <head>, <body>, etc.).

edited Dec 27, 2013 at 9:50

answered Dec 27, 2013 at 9:29

nietonfir

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3 Comments

ryank Over a year ago

I currently have your suggested code uploaded to rgoo.co/calculators/bmr-calculator.php The 66 is cleared to 0 as expected but When values are entered and submit is pressed, the answer does not output

nietonfir Over a year ago

@RyanGoo Obviously not, because your code example is wrong. You use a different variable name for the weight: weightv VS valuec. I fixed this for you in my answer.

ryank Over a year ago

Ahh Thank you! I appreciate the explanation for your solutions as well

The Humble Rat · Accepted Answer · 2013-12-27 09:38:04Z

1

Do something like

$answer = '';
if(isset($_POST["usubmit"]) && $_POST["usubmit"] != '')
{
  $answer = 66 + (6.23*$weightv) + (12.7*$totalheightv) - (6.8*$agev);
}

Then in the html form add a name to your submit button as "usubmit"

<tr class="submit">
   <td colspan="2">
        <input type='submit' name='usubmit'  value='Calculate'/>
   </td>
</tr>

The number 66 is getting shown since on page load it will be assigned to your variable. You can avoid this by adding the condition so that it calculates only when the submit is done.

edited Dec 27, 2013 at 9:38

The Humble Rat

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answered Dec 27, 2013 at 9:32

Abhik Chakraborty

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Comments

SQRCAT · Accepted Answer · 2013-12-27 09:28:53Z

0

Quite simply said, before you echo round($answer) you define a mathematical assignment:

$answer = 66 + (6.23*$weightv) + (12.7*$totalheightv) - (6.8*$agev);

Basing the value on 66. So it is already set, when later on in the code you call

echo($answer);

answered Dec 27, 2013 at 9:28

SQRCAT

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1 Comment

ryank Over a year ago

I understand what you're saying, any suggestions on how to keep the answer field blank until submit is pressed? My knowledge of php functions is minimal.

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