SpaceCats could fail

In video "Shooting Projectiles using SKAction: Part 2 14:37" the slope of a line is calculated

float slope = (position.y - self.position.y) / (position.x - self.position.x);

However, if the user taps on a point directly above the projectile node (i.e. position.x == self.position.x), the slope is undefined.

I haven't tested this yet, but it seems like you'll get a runtime error when the program tries to divide by 0 to calculate the slope.

In this case, it might be easiest to change

if ( position.x <= self.position.x)

into an if and an else if

if ( position.x == self.position.x) //vertical line case
  { 
  // calc distance using something like distanceC = self.parent.frame.size.height + 10 - self.position.y;
  }
else if (position.x < self.position.x )
{
 // calculate like in video
}

I know this isn't exactly correct, but it gives the idea.

I've learned to be careful when working with lines because we've been taught these simple equations that are often so easy that we forget to think about how they work.