The Ternary Operator in PHP

Question

$chow = 3;
echo ($chow == 1) ? "one" : ($chow == 2) ? "two" : "three";

output: three

$chow = 1;
echo ($chow == 1) ? "one" : ($chow == 2) ? "two" : "three";

output: two

Can anyone explain why the output is "two" when $chow = 1 instead of "one"?

So your question is only about the second code block? If yes for what is the first code block? — Rizier123, Feb 25 '15 at 10:03
Never nest ternary operators - it leads to confusing and messy code, and often logic errors as you've seen. — Dan Smith, Feb 25 '15 at 10:08
http://php.net/manual/en/language.operators.comparison.php#example-138 — billyonecan, Feb 25 '15 at 10:09

score 12 · Answer 1 · edited Feb 26 '15 at 09:09

12

This is because the ternary operator (?:) is left associative so this is how it's getting evaluated:

((1 == 1) ? "one" : (1 == 2)) ? "two" : "three"

So 1 == 1 -> TRUE means that then it's:

"one" ? "two" : "three"

And "one" -> TRUE so the output will be:

two

edited Feb 26 '15 at 09:09

Salman A

answered Feb 25 '15 at 10:06

Rizier123

score 6 · Answer 2 · answered Feb 25 '15 at 10:06

6

$chow = 1;
echo ($chow == 1) ? "one" : (($chow == 2) ? "two" : "three");

remember to use brackets when result of operation can be unclear

now output is one

answered Feb 25 '15 at 10:06

Kamil Karkus

1

*Can anyone explain why the output is "two"* This "answer" doesn't answer the question, because it's asking for an explanation not for a solution how to get "one" as output – Rizier123 Feb 25 '15 at 10:10
it's obvious that tenary operator will be evaluated from right to left – Kamil Karkus Feb 25 '15 at 10:20
1

So obvious that you are even wrong! it's from left to right! left associative means from left -> right! – Rizier123 Feb 25 '15 at 10:21

score 0 · Answer 3 · answered Feb 25 '15 at 10:08

0

The operator is confused, you need to put brackets around your second codition. use the code below

$chow = 1;
echo ($chow == 1) ? "one" : (($chow == 2) ? "two" : "three"); //returns 1

Hope this helps you

answered Feb 25 '15 at 10:08

Utkarsh Dixit

*The operator is confused* No! This is very well defined what is happening here! – Rizier123 Feb 25 '15 at 10:09
@Rizier123 actually the operator is thinking "one " as the value if it gets value 2, so putting quotes would make it simple. – Utkarsh Dixit Feb 25 '15 at 10:12

3 Answers3