PHP arithmetic operation where number starts with zero -

i have following code:

$a = 012; echo $a/4; echo '<br>'; echo $a+4; echo '<br>'; echo $a;

this generates following output:

2.5 14 10

however, expect:

3 16 12

why happen when $a starts 0?

as specified @rizier123 must follow integer type doc.

as specified in official documentation of integers type http://php.net/manual/en/language.types.integer.php

integers can specified in decimal (base 10), hexadecimal (base 16), octal (base 8) or binary (base 2) notation, optionally preceded sign (- or +)

$n = 123; // decimal number $n = -123; // negative number $n = 0234; // octal number ...

so in case first number $a = 012 means it's in octal notation.

when division: $a/4 php proceed type juggling converting decimal base , dividing 4

$a = 012; // 10 in decimal base echo $a/4; // 10/4 -> 2.5

note: prior php 7, if invalid digit given in octal integer (i.e. 8 or 9), rest of number ignored

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