[TazeTSchnitzel]

8 is sane here. The + operator adds numbers. It converts the string to a number implicitly in the process. it takes "0x4zz5" and tries to parse as much as possible. Since "z" is not a valid hexadecimal digit, it stops at z, and reads it as 0x4.

Of course, it is better to manually convert.

[PeterisP]

Well, I'd say it's never better to "try to parse as much as you can" and when encountering such an error simply silently give out a nonsense answer.

It's the computer equivalent of a bozo worker who does something random everytime they don't know how to do their job, and then tries to hide any consequences while whistling innocently.

[TazeTSchnitzel]

It's not equivalent at all. It is an expected, clearly-defined behaviour - automatic, silent type conversion, with clear rules on how that type conversion works.

[PeterisP]

I'd bet 1-to-10 that if someone uses '+' operator then that line of code is never expected to encounter "0x4zz5" there. And I'm pretty sure that this addition is not meant to return a number exactly 4 less if it encounters "0z4zz5" instead of "0x4zz5". There is some theoretical chance that it does, but really, it's a lottery-type chance.

The whole total function has something that it's expected to do, some value that it returns in the end - and if it can't do that then any returned value is useless and wrong anyway; and automatic, silent type conversion is the worst possible choice of action, since it not only doesn't work, returning a value that you didn't intend (as other options); but in addition makes the actual bug hard to find and potentially corrupts a lot of stored data before you find the bug.