Simple question about addition of two numbers.

[claudiogc]

Hey, guys!

 

Why the output of my code in both "echo" is only the number "2"?

 

 

<?php
$x = 4;
$y = 2;

//Addition.
echo "Addtion: " . $x + $y . "<br>";
echo 'Addtion: ' . $x + $y . '<br>';
?>

 

Thanks!

[Jacques1]

You somehow assume that addition takes precedence over string concatenation, but that's not the case. They have equal precedence and are evaluated from left to right.

 

It's generally a bad idea to rely on the internal precedence of operators (except maybe for obvious cases like addition and multiplication). Use parentheses. 

Edited August 29, 2014 by Jacques1

[claudiogc]

Problem fixed. Thanks!

 

 

 

They have equal precedence and are evaluated from left to right.

If is the case why is he not showing "Addition: 4"? Because he should concat "Addition" with "4" and after that i have no idea.

Edited August 29, 2014 by claudiogc

[kicken]

If is the case why is he not showing "Addition: 4"? Because he should concat "Addition" with "4" and after that i have no idea.

If you evaluate it one operator at a time and sub the results into the original equation you can see what happens.

echo 'Addtion: ' . $x + $y . '<br>';

Evaluate the first . operator, result is: 'Addition: 4', so then you have:

echo 'Addtion: 4' + $y . '<br>';

Evaluate the + operator. PHP try and convert the first operand to a number but since the string is not a valid number you get zero. Now you have:

echo 2 . '<br>';

Which gives you a final output of '2<br>';

[claudiogc]

 

 

PHP try and convert the first operand to a number but since the string is not a valid number you get zero.

Did not understand this part.

"PHP try and convert the first operand to a number"

The number 2? Because the real first operand of the operation, number 4, already is part of the other string. What happened to "+"?

 

"but since the string is not a valid number you get zero."

What string?

[kicken]

The + operator applies to 'Addition: 4' and 2. 'Addition: 4' is a string, not a number so PHP will attempt to convert it. Since it is not possible to convert it however you end up with zero so the end result is you have 0 + 2.

[Psycho]

Step 1:
echo [ "Addtion: " . $x ] + $y . "<br>";
 
PHP CONCATENATES the String "Addition" and the number 4 creating the string "Addition: 4", which results in:
echo "Addtion: 4" + $y . "<br>";
 
 
//Step 2:
echo [ "Addtion: 4" + $y ] . "<br>";
 
PHP ADDS the string "Addition: 4" with the number 2 Since the string is not a number, PHP converts it to one. Since it begins with an alpha character it converts it to 0. Thus, you get [ 0 + 2]. Result:
echo 2 . "<br>";
 
Step 3:
echo [ 2 . "<br>" ];
 
PHP CONCATENATES the Number 2 and the string "<br>"
Result
 
echo "2 <br>";

Edited August 29, 2014 by Psycho