In php why is it the case that 10 & 10 == 10 returns 0?

Question

I am messing with PHP operators and I cannot understand why

10 & 10 == 10

returns 0. This should compare 10 to 10 which is true right?

Answer 1

The comparison operators have higher precedence than the bitwise operators, so that expression is evaluated as:

10 & (10 == 10)

10 == 10 evaluates to true, so you get 10 & true .

The bitwise & converts the true to 1 , so you get 10 & 1 which is 0 .

Notice that 11 & 10 == 10 results in 1 , since 11 & 1 === 1 .

Answer 2

Because the == operator is parsed before the & operator because it is judged more important by the parser. But you can override the default operator evaluation order with brackets:

(10 & 10) == 10

Answer 3

Your expression is similar to:

( 10 & 10 == 10 ) = ( 10 & (10 == 10) ) = ( 10 & (true) ) = 0

Precedence of == is from right (higher) it will be evaluated before &

Answer 4

& is used for bit operations and == for comparison so be careful ... Here is an example :

echo((10 & 12));

Is printing 8 because 10 = 00001010 and 12 = 00001100 and 00001010 & 00001100 = 00001000 = 8

Answer 5

Are you comparing if 10 is the same as 10?

IF (10 == 10) {
     // condition code
}

or 10 and 10 are both true

IF (10 && 10) {
    // condition code
}

Answer 6

& is the bitwise operator in php and == tests for equality.

Since the precedence, see http://php.net/manual/en/language.operators.precedence.php , of == is higher than &, your test is the same as 10 & (10 == 10)

10 == 10 will return boolean true (same as a 1 in binary)

Now we are left with 10 & true which is the same as 10 & 1

the bitwise operator, &, looks at each bit of the 2 values and sets the corresponding bit in the result to 1 if they are both 1 and 0 otherwise, eg:

5 (101) & 3 (011) = 1 (001)
5 (101) & 2 (010) = 0 (000)
6 (110) & 4 (100) = 4 (100)

Therefore 10 (1010) & 1 (0001) = 0 (0000) so the result of 10 & 10 == 10 is 0!

If you just want to compare 10 to 10 then use 10 == 10