I never ever had problems with it in C. I actually had a problem with it in another language (might have been a BASIC) where = was contextual, so one could do "a = 10" and then somewhere down the line "if x = 5 then". I used == and couldn't figure out what was wrong for nearly 5 minutes (I think it was recognising (or not) as an unexpected token).

= and == should have different meanings.

I also like how JavaScript has ===, although it is a little superfluous.

Interestingly PostgreSQL's pl/pgsql does that.

There are two operators, equality = and assignment :=

But where it is clear that assignment was meant, = is treated as assignment. this means you can:

    a = 5; -- exactly equivalent to a := 5 here
    if a = 6 then
        raise exception 'this should never happen';
    end if;

Interestingly this is entirely a Postgres-ism. Oracle's PL/SQL offers no such "feature."