C++ “OR” operator

Question

can this be done somehow?

if((a || b) == 0) return 1;
return 0;

so its like...if a OR b equals zero, then...but it is not working for me.

Answer 1

You have to specify the condition separately each time:

if (a == 0) || (b == 0))
    bla bla;

When you do

if ((a || b) == 0)
    bla bla;

it has a different meaning: (a || b) means "if either a or b is non-zero (ie. true), then the result of this expression is true". So when you do (a||b) == 0, you are checking if the result of the previously explained expression is equal to zero (or false).

Answer 2

Fun with templates:

template <typename T>
struct or_t
{
  or_t(const T& a, const T& b) : value1(a), value2(b)
  {
  }

  bool operator==(const T& c)
  {
    return value1 == c || value2 == c;
  }

private:
  const T& value1;
  const T& value2;
};

template <typename T>
or_t<T> or(const T& a, const T& b)
{
  return or_t<T>(a, b);
}

In use:

int main(int argc, char** argv)
{
  int a = 7;
  int b = 9;

  if (or(a, b) == 7)
  {
  }

  return 0;
}

It performs the same comparison you would normally do, though, but at your convenience.

Answer 3

You need to write the full expression:

(a==0)||(b==0)

And in the second code:

if((p1.distanceFrom(l.p1)<= r) || (p1.distanceFrom(l.p2)<=r) )
    return 1;

If you do ((a || b) == 0) this means "Is the logical or of a and b equal to 0. And that's not what you want here.

And as a side note: the if (BooleanExpression)return true; else return false pattern can be shortened to return BooleanExpression;

Answer 4

C++ isn't that smart. You have to do each comparison manually.

bool Circle2::contains(Line2 l) {
if((p1.distanceFrom(l.p1) <= r) || (p1.distanceFrom(l.p2) <= r)) return 1;
    return 0;
}

Answer 5

Your condition should be (a == 0 || b == 0) or (p1.distanceFrom(l.p1) <= r || p1.distanceFrom(l.p2)) <= r)

Answer 6

If you have lot of that code, you may consider a helping method:

bool distanceLE (Point p1, Point p2, double threshold) {
    return (p1.distanceFrom (p2) <= threshold)
}

bool Circle2::contains (Line2 l) {
    return distanceLE (p1, l.p1, r) && distanceLE (p1, l.p2, r);
}

If you sometimes have <, sometimes <=, >, >= and so on, maybe you should pass the operator too, in form of a function.

In some cases your intentions by writing this:

if ((a || b) == 0) return 1;
return 0;

could be expressed with an bitwise-or:

if ((a | b) == 0) return 1;
return 0;

and simplified to

return  ! (a | b);

But read up on bitwise operations and test it carefully. I use them rarely and especially I didn't use C++ for some time.

Note, that you inverted the meaning between your examples 1 and 2, returning true and false in the opposite way.

And bitwise less-equal doesn't make any sense, of course. :)