The coding regarding the distance formula

Hey Liam,

I hope you didn't give up yet!

First of all, the all Cartesian difference, power and square root are more related to math than programming itself. So don't worry if you don't get everything right away!

When I was at your age, I learned Pascal programming language all by myself from the book. I had no one to ask for help, Internet was not big thing back then and I didn't had access to it, also Wikipedia and Treehouse didn't exist yet!

What I'm trying to say here is: I know it all can be little confusing. And it is quite painful when you discover more and more pitfalls along the way. But that is normal, give it a time, do your research and eventually you will figure all out.

Now back to your question...

Code you actually posted in your question isn't correct:

  int yDiff = X - x;
  int xDiff = Y - y;

If you look little closer you will realize it should be:

  int xDiff = X - x;
  int yDiff = Y - y;

And if you check video, that is exactly what Jeremy has on the screen :)

It might seem to be small mistake, but from now on I'm not even sure if you understand what you are asking for.

Next topic - difference (with simple math)

To help you out a little, let's talk about difference and how it is important. Please consider following example:

Let's say you are 15 years old. I'm 35 years old. What is our age difference? How to calculate it?

Let's try to somehow code it:

int ageOfLiam = 15;
int ageOfJarek = 35;

Now let's see how we can calculate difference:

int ageDifference1 = ageOfLiam - ageOfJarek; // it gives -20
int ageDifference2 = ageOfJarek - ageOfLiam; // it gives 20

Ok, so as you can see we have 2 possibilities, but which one is correct? The real answer is both!

But wait! One is negative? How is that possible?

Well it's actually easy, first difference called ageDifference1 tells us how much your age is before mine (in other words how many years I need to get to be at your age). Second one called ageDifference2 tells us how much my age is before yours, in other words: how many years you need to be at my age.

As you can see from above example, we count difference by subtracting one thing from another. Depending on the order we will get either positive or negative number, but it still will be the same value (regardless of sign).

That is exactly how we tell the distance between two different points (like cities, trees, roads, etc.). We subtract their position (at least in single dimension).

Important note: as you should know, distance needs to be positive. There is no much use of negative distance in our real world.

Back to Cartesian formula

Normally it would require to use something called absolute value, to properly get positive distance value after subtraction.

But with formula for two dimensional distance (2D) we are using power of 2 on both subtractions. Using power of two on any integral number (positive or negative) gives always positive value.

Square root is backward operation to power of 2.

At this point on, you don't really need to understand why and how this formula works. You only need to properly code it :)

But as you will discover in future, you can't be a very good Programmer(or even decent) without proper math skills. Solution to many problems you will face in programming world comes back to simple (or not so simple) math.

And remember, it is not an excuse if it wasn't at school. If it wasn't yet, it may either never be, so it is your responsibility to gain that knowledge and clear all gaps. There are probably tons of useful books you could choose from to help you out in either math or programming. So pump up your math skills and get back to coding (or learning how to).

Good luck!

Cheers! Jarek

I struggle with some of the maths too, try khan academy for vids on maths. I need a visual breakdown so that helps, math.pow is taking a number to the power of something.

the number is just that a number, the power is the number of times you are going to multiply that number by its self. so

2 to the power of 2 is 2 x 2

2 to the power of 3 is 2 x 2 x 2 so multiplied by 2 three times, the power of three.

2 to the power of 5 would be 2 x 2 x 2 x 2 x 2.

Lots of coding has only basic maths, you can learn as you go. dont let it stop you.

To clarify, the capital Y does not refer to the variable being passed in, but it is an instance variable when the class gets constructed - this is why it is common to put "this" in front of variables to denote that they are instance variables.

when we say: int xDiff = Y - y; the capital Y refers to: public readonly int Y

Y-y just means whatever is stored in Y minus whatever is stored in y.