Readability a=b=c or a=c; b=c;?

I happen to prefer the chained version, but it’s completely a matter of preference.

Please note, however, that

a = b = c = 0;

is equivalent to:

c = 0;
b = c;
a = b;

and not

a = 0;
b = 0;
c = 0;

(not that it should matter to you which assignment happens first)