[Derision]

I may be misunderstanding your comment, but quest::istaskcompleted() returns 0 for false and 1 for true, so:

if(quest::istaskcompleted(20)) {
    // do something
}

is the same as:

if(quest::istaskcompleted(20) != 0) {
    // do something
}

The first form is just shorthand.