Calculation in php giving error

Question

On my site I have the following code to calculate discounts:

$valor_a_ser_calculado =$_POST['loc']; // valor original
$quantos_porcento = 75/100; //isso equivale a 7% 
$loc = $quantos_porcento * $valor_a_ser_calculado . "\n";

only the following mistake is making:

PHP Warning:  A non-numeric value encountered in /home/jp/public_html/orcamento.php on line 6

I’d like to know how to fix it

Answer 1

You have two immediate problems in the code: You are not checking whether the POST value is correct, and mixing multiplication with concatenation. Test with this:

$valorasercalculado = $_POST['loc']; // valor original
echo "Valor original: $valorasercalculado <br>";

$quantos_porcento = 75/100; //isso equivale a 7.5% 
echo "Porcentagem: $quantosporcento <br>";

$loc = $quantos_porcento * $valor_a_ser_calculado;
echo "Resultado: $loc <br>";

In this case, you will only have warnings if any of the values are not numerical.

The ideal would be to rethink something along these lines:

$valorasercalculado = isset($_POST['loc']) ? $_POST['loc'] : 0;

Or even

if (!isset($_POST['loc'])) die 'Valor não fornecido';

right at the beginning of the code.

As well remembered by fellow @Rafaelsalomao, PHP has a specific function to test if a value is numerical. Joining the two ideas:

if (!isset($_POST['loc'])) die 'Valor não fornecido';
if (!is_numeric($_POST['loc'])) die 'O valor precisa ser numérico';

(remembering that ! before the function means "not", in the above cases, if the value is NOT set, the script stops. If the value is NOT numerical, the script also stops).

Handbook:

http://php.net/manual/en/function.isset.php

http://php.net/manual/en/function.is-numeric.php