My variable always becomes a zero

Question

I have a problem with my C++ code where Im doing two steps in one with regards to pythagoras.

Im getting the length of a and b at the same time as doing the pythagoras function but my variable always equals 0 even though the X and Y points show up with their respective values.

Unfortunatly due to this when square rooting the resut it procceds with an error as you cannot square root 0.

It looks kinda complicated but this was the neatest I could get it

hypPrevious = ( 
                ( *(previousCalcp->getX()) - *(currentCalcp->getX()) ) 
                *   
                ( *(previousCalcp->getX()) - *(currentCalcp->getX()) )
              ) 
              +
              ( 
                ( *(currentCalcp->getY()) - *(previousCalcp->getY()) ) 
                *   
                ( *(currentCalcp->getY()) - *(previousCalcp->getY()) )
              );

If the current X and previous X are the same number you will get 0. 0 * 0 is 0. — Elliott Frisch, Apr 18 '14 at 17:05
Check if the pointers are equal: previousCalcp == currentCalcp. And wy do you use pointers? — , Apr 18 '14 at 17:06
I thought that but If it helps the co ordinates should be like this current X: 4 Y: 8 previous Y: X 8 Y: 9 — Harvey, Apr 18 '14 at 17:07
I'll check the pointers, and I have to use pointers as its part of a method which links to another class. just passing a pointer is faster than a whole object — Harvey, Apr 18 '14 at 17:08
Faster in what way? Using pointers makes your code harder to read and more likely to have bad pointers. — Rob K, Apr 18 '14 at 17:11
Just to be sure, because this is unusual. Do functions getX() and getY() return pointers to coordinates? — Adam Wulkiewicz, Apr 18 '14 at 17:13
why don't store the values instead of wasting time recalculating the results like that? — phuclv, Apr 18 '14 at 17:19

Danvil · Accepted Answer · 2014-04-18T17:21:21.503

1

With the information you gave us, the best advice I can give you is rewriting your code and add a debugging line to check what is going wrong:

int x1 = *(previousCalcp->getX());
int y1 = *(previousCalcp->getY())
int x2 = *(currentCalcp->getX());
int y2 = *(currentCalcp->getY());
int dx = x1 - x2;
int dy = y1 - y2;
hypPrevious = dx*dx + dy*dy;
std::cout << "(" << x1 << "," << y1 << ") and (" << x2 << "," << y2 << ") resulted in " << hypPrevious << std::endl;

Don't forget to change the type int to whatever you are using in your code.

edited Apr 18 '14 at 17:21

answered Apr 18 '14 at 17:13

Danvil

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This is probably a good idea, Its getting a little confusing... Sorry if this sounds silly but i've used cout many times, but what does it do when you put 'std::' in front? – Harvey Apr 18 '14 at 17:16
You have to add `std::` when you do not use `using namespace std;` and minimize namespace pollution. – Danvil Apr 18 '14 at 17:20

My variable always becomes a zero

1 Answers1