what is 0050 and why echo 0050 result 40 [duplicate]

Answer 1

0050 is a value in octal which is a base 8 number system. when printed the number is first converted to a decimal representation and printed.

Answer 2

050 is an octal (base 8) literal for 40 (base 10).

http://php.net/manual/en/language.types.integer.php