Question

How can I check a value entered in a field on my form is a number?

ex:

$values = array(1,20,10); 

Answer 1

you can use function :
is_numeric() — Finds whether a variable is a number or a numeric string ..

for example :

<?php
$tests = array(
    "42", 
    1337, 
    "1e4", 
    "not numeric", 
    array(), 
    9.1
);

foreach ($tests as $element) {
    if (is_numeric($element)) {
        echo "'{$element}' is numeric", PHP_EOL;
    } else {
        echo "'{$element}' is NOT numeric", PHP_EOL;
    }
}
?>

The above example will output:

'42' is numeric
'1337' is numeric
'1e4' is numeric
'not numeric' is NOT numeric
'Array' is NOT numeric
'9.1' is numeric

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