PHP - Check for positive / negative numeric strings

Question

I'd like to know what is the best way to check whether a numeric string is positive or negative.

I am using this answer on S.O but I am not able to determine whether a number with decimals is + or -

For example :

function check_numb($Degree){
  if ( (int)$Degree == $Degree && (int)$Degree > 0 ) {
    return 'Positive';
} else {
    return 'Negative';
  }
}

print check_numb("+2"); // returns Positive
print check_numb("+2.0"); // returns Positive
print check_numb("+2.1"); // returns Negative ??
print check_numb("+0.1"); // returns Negative ??
print check_numb("-0.1"); // returns Negative

It seems when a decimal is added it returns false. How do you properly check for positive strings > +0.XX and negative < -0.XX which 2 decimals..

Thanks!

(int)"+2.1" == 2 and 2 != "+2.1" - For ALL numbers, if it is < 0 it is negative and if it is > 0 it is positive. — AbraCadaver
– AbraCadaver, Commented Mar 19, 2015 at 17:08
I understand but given a $numb= "+0.8" ; then (int)$numb returns 0 instead of 0.8, it returns negative. how could I return the (int) with decimals, does this sounds logic? — Awena
– Awena, Commented Mar 19, 2015 at 17:14

Clément Malet · Accepted Answer · 2015-03-19 17:14:45Z

3

Considering the given input, why not :

$number = '+2,33122';
$isPositive = $number[0] === '+' ? 'Positive' : 'Negative';
// Positive

$number = '-0,2';
$isPositive = $number[0] === '+' ? 'Positive' : 'Negative';
// Negative

Here is a more generic code, working even if the sign is removed from your input :

function checkPositive ($number) {
   if (!is_numeric(substr($number, 0, 1))) {
       $sign = substr($number, 0, 1);
       return $sign == '+';
   }
   return $number > 0;
} 


$number = '+2,33122';
var_dump(checkPositive($number));
// true

$number = '-2,33122';
var_dump(checkPositive($number));
// false

$number = '2,22';
var_dump(checkPositive($number));
// true

edited Mar 19, 2015 at 17:14

answered Mar 19, 2015 at 17:05

Clément Malet

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2 Comments

Awena Over a year ago

I assume this method will always require numeric string to start either with the + or - signs. Right ?

Clément Malet Over a year ago

@Awena Yes. I added a function that will work in any case : with or without a sign before the numeric value

AbraCadaver · Accepted Answer · 2015-03-19 17:28:02Z

2

Your problem is because: (int)"+2.1" == 2 and 2 != "+2.1". For ALL numbers, if it is < 0 it is negative and if it is > 0 it is positive. If it is == 0, then it is obviously 0 which is unsigned.

function check_numb($Degree){
  if ( $Degree > 0 ) {
    return 'Positive';
} elseif( $Degree < 0 ) {
    return 'Negative';
  }
}

edited Mar 19, 2015 at 17:28

answered Mar 19, 2015 at 17:16

AbraCadaver

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