I really don't understand why you want (c2 - c1 == 0)insteadc1 == c2
why not go
if ((c1 == c2) && (c1 != c3)){
do_stuff();
}
or
if ((c1 != c3) && (c1 == c2)){
do_stuff();
}
way
As a side note, there is no penalty or advantage when switching c1 to c2 anywhere. From the above, at first the most probable failure condition is somewhat more efficient, because the second condition will not be evaluated if the first is not fulfilled.
: -, .
: , , ( ), . c1 c2 , c3, , . . , . - , .