Well, with stuff your refering too where is the full code:
CGPoint p2; //[1]
CGPoint p1;
//Assign the coord of p2 and p1...
//End Assign...
CGFloat xDist = (p2.x - p1.x); //[2]
CGFloat yDist = (p2.y - p1.y); //[3]
CGFloat distance = sqrt((xDist * xDist) + (yDist * yDist)); //[4]
The distance is the variable distance.
What is going on here:
You can't really make a CGPoint be the distance, distance doesn't have an x and y component. It is just 1 number.
If you think CGPoint is a unit of measurement (for example feet is a unit of measurement) it is not.