What could be the output of echo ('True'?(true?'t':'f'):'False'); And explain why?

Question

Possible Duplicate:
What is the PHP ? : operator called and what does it do?

i was interviewed with a very basic question of PHP which was like:

echo ('True' ? (true ? 't' : 'f') : 'False');

Can Someone explain the details of the output it will yield?

Thanks

Hope hard they don't have that kinda code in their production — Andreas Wong, Feb 07 '12 at 07:13
How the heck is this the Duplicate? of the question you are referring, If you are talking about reference of concept then Already there are hell lot questions been asked before and every new question can become the duplicate of those available conceptually connected ones — OM The Eternity, Feb 07 '12 at 07:16

score 4 · Answer 1 · answered Feb 07 '12 at 07:11

4

Looking at this version should make it clear:

if('True'){ // evaluates true
    if(true){ // evaluates tre
        echo 't'; // is echo'd
    }else{
        echo 'f';
    }
}else {
    echo 'False';
}

answered Feb 07 '12 at 07:11

konsolenfreddy

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1

Did you try running it in the console? Because you're wrong. What makes you think `if(true)` somehow evaluates false? – user229044 Feb 07 '12 at 07:13
2

`if(true){ // evaluates false` ??? – dfsq Feb 07 '12 at 07:13
sorry, wrote the answer before running it. Very early in the morning, but corrected the answer – konsolenfreddy Feb 07 '12 at 07:15

Code Lღver · Accepted Answer · 2013-04-21T05:31:02.687

This will echo t.

Because of first it will check the first condition that will give true. and after that in next condition it again give true and execute the first condition that is t.

In if and else condition it will be write as follow:

if('True') { //condition true and go to in this block
   if(true){ //condition true and go to in this block
      echo 't'; // echo t
   } else {
      echo 'f';
   }
} else {
   echo 'False';
}

Salman A · Answer 3 · 2018-11-12T10:51:12.520

4

A non-empty string is considered a truthy value except the string "0". PHP evaluates

'True' ? (true ? 't' : 'f') : 'False'

from left to right as follows:

The expression 'True' is evaluated as a boolean true
Next, the expression following the ? is evaluated
- The expression true is... true!
- The expression following the ? is returned, which is t

Surprisingly, you'll still get t if the expression was:

echo 'False' ? (true ? 't' : 'f') : 'False'

edited Nov 12 '18 at 10:51

answered Feb 07 '12 at 07:23

Salman A

262,204
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Why would "The expression 'True' is evaluated as boolean true"? its a string right?? – OM The Eternity Feb 07 '12 at 07:25
To process a [ternary operator](http://www.php.net/manual/en/language.operators.comparison.php#language.operators.comparison.ternary) PHP expects (and converts if necessary) the first expression to true or false. – Salman A Feb 07 '12 at 07:29
So its PHP's own understanding, whom to read true and fase? no matter the expression is a string? – OM The Eternity Feb 07 '12 at 07:33
1

The "understanding" is explained [here](http://www.php.net/manual/en/types.comparisons.php) -- see the section _Comparisons of $x with PHP functions_ and the column _if($x)_. – Salman A Feb 07 '12 at 07:51

score 3 · Answer 4 · answered Feb 07 '12 at 07:14

3

As 'True' is Evaluated as true

if('True'){
    if(true){
        echo 't';
    }else{
        echo 'f';
    }
}else{
    echo 'False';
}

answered Feb 07 '12 at 07:14

amd

20,637
6
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score 3 · Answer 5 · answered Feb 07 '12 at 07:15

3

The inner bracket will be executed first true?'t':'f' it will return 't' that is a string

Now outer condition will check for echo ('True' ? 't' : 'False'). Here 'True' is a "non empty string"(implicitly casted to TRUE), so it evaluate to true, and will return 't'.

Final code will be echo ('t') which will simply echo t

answered Feb 07 '12 at 07:15

Uday Sawant

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Exactly they answered me like answer is "t" but didn't gave me the reason... But I still wonder why inner loop is executed first? – OM The Eternity Feb 07 '12 at 07:20
Oh Yes I evaluated using the answers to the question, Understood the evaluation order now.. Thanks – OM The Eternity Feb 07 '12 at 07:21
Its a evaluation order, whatever you put inside brackets will be executed first – Uday Sawant Feb 07 '12 at 07:22
The inner bracket will _not_ be executed first! – Salman A Feb 07 '12 at 07:32
@Salman if the expression in if else format, then dont you think that inner loop will be executing first? – OM The Eternity Feb 07 '12 at 07:35
@SalmanA Sorry if i am wrong, but then how will you get value for true case of outer bracket? – Uday Sawant Feb 07 '12 at 07:40

score 3 · Answer 6 · answered Feb 07 '12 at 07:17

echo ( // will echo the output
  'True'? // first ternary operation 'True' is considered true
    (true? 't':'f') // will go here for the second ternary operation
                    // true is also evaluated as true so it will echo 't'

  : 'False'); // never goes here

score 3 · Answer 7 · answered Feb 07 '12 at 07:22

This:

'True'?(true?'t':'f'):'False'

May be written as

// Will always be true if String is not an Empty string. 
if('True'){ 
   // if (true) will always enter
   if(true){ 
      // t will be the output
      echo 't'; 
   }else{
      echo 'f';
}
else {
    echo 'False';
}

What could be the output of echo ('True'?(true?'t':'f'):'False'); And explain why?

7 Answers7