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, Mar 19 '15 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, Mar 19 '15 at 17:14

Clément Malet · Answer 1 · 2015-03-19T17:14:45.520

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 '15 at 17:14

answered Mar 19 '15 at 17:05

Clément Malet

5,062
3
29
48

I assume this method will always require numeric string to start either with the + or - signs. Right ? – Awena Mar 19 '15 at 17:08
@Awena Yes. I added a function that will work in any case : with or without a sign before the numeric value – Clément Malet Mar 19 '15 at 17:15

AbraCadaver · Accepted Answer · 2015-03-19T17:28:02.207

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 '15 at 17:28

answered Mar 19 '15 at 17:16

AbraCadaver

78,200
7
66
87

PHP - Check for positive / negative numeric strings

2 Answers2