php - why there is a difference between below given output? -

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$y = 07; echo 'y: '.$y; // result 7 $y = 08; echo 'y: '.$y; // result 0

view demo

:edit:

one more similar 

$y = 013; echo $y + 5; //this result in 16

i can not figure out how ans 16? can 1 help?

part 1

the rules parsing explained in integers documentation.

in php number starting 0 assumed in octal. because 08 in octal isn't valid getting 0.

part 2

the same issue in play, 013 in octal 11 in decimal , 11 + 5 = 16


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