Question

I’m sort of a newbie–please don’t hate.

The method compiles, but I’m not sure how to actually retrieve the float value (i.e. the distance between the two points) that the method returns (or should return rather).

-(float)findDistanceBetween:(Coordinate *)a and:(Coordinate *)b
{
//distance formula: 
//sqrt( (x2 - x1)^2 + (y2 - y1)^2 )

float resultDistance; 

resultDistance = sqrt( pow((b.latitude - a.latitude), 2) + pow((b.longitude - a.longitude), 2));

return resultDistance;  
}

//Somewhere else...

float theDistanceBetween; 

//Below is incorrect:

theDistanceBetween = [findDistanceBetween: location1 and: location2]; 

Thanks

Answer 1

Is findDistanceBetween:and: defined in an @implementation block? Your code should look something like

   // in the .h file

   @interface MyClass : NSObject

   // declaration of the method
   - (float)findDistanceInBetween:(Coordinate *)a and:(Coordinate *)b;
   @end

   // in the .m file

   @implementation MyClass

   // definition of the method
   - (float)findDistanceBetween:(Coordinate *)a and:(Coordinate *)b {
       return sqrt(powf(a.x - b.x, 2.f) + powf(a.y - b.y, 2.f));
   }
   @end

   // then somewhere else that needs to calculate the difference:
   // (assume coord_a and coord_b already exist)

   // create an instance of MyClass
   MyClass *myInstance = [[MyClass alloc] init];

   // send the `findDistanceBetween:and:` message to the instance
   float distance = [myInstance findDistanceBetween:coord_a and:coord_b];

   // when you're done with the instance, you need to clean up
   [myInstance release];

It may make more sense to put these types of methods on the Coordinate class itself so you can just do something like:

   Coordinate *coord_a = <get the coordinate from somewhere>;
   Coordinate *coord_b = <get the coordinate from somewhere>;

   float distance = [coord_a distanceFrom:coord_b];
   float angle = [coord_a angleTo:coord_b];

Don’t worry about anyone hating, we were all new at this once. 🙂