Question

It is my first question, so hi all..

Is it possible to satisfy this condition?
Where $a and $b are some defined variables

if(!is_numeric($a * $b.'')) { ... }

EDIT: Second conditon

$a * $b can't be INF

Answer 1

You can satisfy the condition with specific values of $a and $b. For example, $a = $b = 1e200, or $a = 1e400, $b = 0.

If the product of $a and $b overflows to infinity or is a not-a-number, the concatenation with an empty string will produce the string INF or NAN:

php > var_export(1e200*1e200);
INF
php > var_export(is_numeric(1e200*1e200));
true
php > var_export(is_numeric(1e200*1e200.''));
false

php > var_export(1e400*0);
NAN
php > var_export(is_numeric(1e400*0));
true
php > var_export(is_numeric(1e400*0 .''));
false