Uncaught DivisionByZeroError: Division by zero in BMI Calculator - php

Question

I tried to make BMI Calculator using php where the student is needed to input their names, matric number, height and weight to know their BMI.
However ,I got this error
Fatal error: Uncaught Division By Zero Error: Division by zero
but it disappeared when I put the value inside.
I have no idea what's wrong with my code.
HMTL Form
<form>
Enter your name : <input type = "text" name = "student_name" value = "<?php echo #$_GET["student_name"]?>"> <!--Accepts name-->
<br>
Enter matric number : <input type = "text" name = "student_matricno" value = "<?php echo #$_GET["student_matricno"]?>"> <!--Accepts Matric Number-->
<br>
Enter weight (in KG): <input type ="text" name = "student_weight" value = "<?php echo #$_GET["student_weight"]?>"> <!--Accepts student's weight-->
<br>
Enter Height (in Meters): <input type ="text" name = "student_height" value = "<?php echo #$_GET["student_height"]?>"> <!--Accepts student's height-->
<br>
<input type = "submit">
</form>
<table> <!--Create table and display the values inputted by the user-->
<tr>
<th colspan ="2">Student Information</th>
</tr>
<tr>
<td>Name</td>
<td><?php echo #$_GET["student_name"]?></td>
</tr>
<tr>
<td>Matric Number</td>
<td><?php echo #$_GET["student_matricno"]?></td>
</tr>
<tr>
<td>Weight</td>
<td><?php echo #$_GET["student_weight"]?> kg</td>
</tr>
<tr>
<td>Height</td>
<td><?php echo #$_GET["student_height"]?> meters</td>
</tr>
</table>
PHP code
$weight = #$_GET["student_weight"];
$height = #$_GET["student_height"];
function myBMI($weight,$height) //function to calculate BMI
{ $BMI = 0;
$BMI = $weight / ($height * $height);
return $BMI;
}
$BodyMassIndex = number_format(myBMI($weight,$height),2); //convert the calculated values into 2 decimal places
//conditions for BMI
if ($BodyMassIndex < 18.5)
{
$status = "Underweight";
}
else if($BodyMassIndex < 21)
{
$status = "Normal";
}
else if($BodyMassIndex < 26)
{
$status = "Overweight";
}
else
{
$status = "OBESE";
}
echo "My BMI is" .$BodyMassIndex. "and I am ".$status;
?>
</html>```

Answer 1

The function does no sanity checks on the input values supplied. In the below a very simple test is done to ensure that neither value is zero (empty) and will print an alternative message if this is so. Using an elvis operator when assigning the values to $height & $weight sets them at zero if they are not present in the GET request at that stage which ensures a zero value is passed to the function.
<?php
$weight = $_GET["student_weight"] ?: 0;
$height = $_GET["student_height"] ?: 0;
function myBMI( $weight=0,$height=0 ){
return !empty($weight) && !empty( $height ) ? $weight / ( $height * $height ) : 0;
}
$BodyMassIndex = number_format( myBMI( $weight, $height ),2 );
if ($BodyMassIndex < 18.5) {
$status = "Underweight";
}else if($BodyMassIndex < 21){
$status = "Normal";
}else if($BodyMassIndex < 26){
$status = "Overweight";
}else{
$status = "OBESE";
}
if( $BodyMassIndex > 0 ) echo "My BMI is" .$BodyMassIndex. "and I am ".$status;
else echo "<span style='color:red'>Please fully complete the form to calculate your BMI</span>";
?>