nested php ternary trouble: ternary output != if - else [duplicate] - php

Question

This question already has answers here:
Stacking Multiple Ternary Operators in PHP
(11 answers)
Closed 2 years ago.
I am fairly capable at using the PHP ternary operator. However I have hit a roadblock at trying to figure out why the code below does not match the if-else equivalent structure. The test was run three times on different numbers. The output for each structure is below the code.
Ternary:
$decimal_places = ($max <= 1) ? 2 : ($max > 3) ? 0 : 1;
Ternary Output:
max: -100000 decimal: 0
max: 0.48 decimal: 0
max: 0.15 decimal: 0
If-Else
if($max <= 1)
$decimal_places = 2;
elseif($max > 3)
$decimal_places = 0;
else
$decimal_places = 1;
If-Else Output:
max: -100000 decimal: 2
max: 0.48 decimal: 2
max: 0.15 decimal: 2
Can anyone please tell me why the these two control stuctures do not output the same data?

Answer 1

Your right-hand-side ternary expression needs to be wrapped in parentheses so it'll be evaluated by itself as a single expression:
$decimal_places = ($max <= 1) ? 2 : (($max > 3) ? 0 : 1);
// Another way of looking at it
$decimal_places = ($max <= 1)
? 2
: (($max > 3) ? 0 : 1);
Otherwise your ternary expression is evaluated from left to right, resulting in:
$decimal_places = (($max <= 1) ? 2 : ($max > 3)) ? 0 : 1;
// Another way of looking at it
$decimal_places = (($max <= 1) ? 2 : ($max > 3))
? 0
: 1;
Which, translated to if-else, becomes this:
if ($max <= 1)
$cond = 2;
else
$cond = ($max > 3);
if ($cond)
$decimal_places = 0;
else
$decimal_places = 1;
Therefore $decimal_places ends up as 0 for all values of $max except 2, in which case it evaluates to 1.

Answer 2

The code is executed as
$decimal_places = (($max <= 1) ? 2 : ($max > 3)) ? 0 : 1;
so you'll never get 2 and 1 only when 1 < $max <=3. This is because the conditional operator is left-associative. Solution: Place parentheses to make sure the order you want is coded:
$decimal_places = ($max <= 1) ? 2 : (($max > 3) ? 0 : 1);

Answer 3

Just put the parenthesis and you would be fine, like this:
$decimal_places = ($max <= 1) ? 2 : (($max > 3) ? 0 : 1);

Answer 4

As others pointed out, use paranthesis.
However, if you actually want to make it readable, what about this:
$decimal_places =
($max <= 1) ? 2 : (
($max > 3) ? 0 : (
1
));
This still looks super awkward, but this awkwardness has a regular shape, so it's easier to live with.
$drink = 'wine';
return
($drink === 'wine') ? 'vinyard' : (
($drink === 'beer') ? 'brewery' : (
($drink === 'juice') ? 'apple tree' : (
($drink === 'coffee') ? 'coffeebeans' : (
'other'
))));
You could of course omit the last pair of brackets, but that would make it less regular-looking.