ARRAYS DEBUGGING incorrect outputs, complex algorithm - c++

Question

I made this algorithm, i was debugging it to see why it wasnt working, but then i started getting weird stuff while printing arrays at the end of each cycle to see where the problem first occurred.
At a first glance, it seemed my while cycles didn't take into consideration the last array value, but i dunno...
all info about algorithm and everything is in the source.
What i'd like to understand is, primarily, the answer to this question:
Why does the output change sometimes?? If i run the program, 60-70% of the time i get answer 14 (which should be wrong), but some other times i get weird stuff as the result...why??
how can i debug the code if i keep getting different results....plus, if i compile for release and not debug (running codeblocks under latest gcc available in debian sid here), i get most of the times 9 as result.
CODE:
#include <iostream>
#include <vector>
/*void print_array
{
std::cout<<" ( ";
for (int i = 0; i < n; i++) { std::cout<<array[i]<<" "; }
std::cout<<")"<<std::endl;
}*/
///this algorithm must take an array of elements and return the maximum achievable sum
///within any of the sub-arrays (or sub-segments) of the array (the sum must be composed of adjacent numbers within the array)
///it will squeeze the array ...(...positive numbers...)(...negative numbers...)(...positive numbers...)...
///into ...(positive number)(negative number)(positive number)...
///then it will 'remove' any negative numbers in case it would be convienent so that the sum between 2 positive numbers
///separated by 1 negative number would result in the highest achievable number, like this:
// -- (3,-4,4) if u do 'remove' the negative number in order to unite the positive ones, i will get 3-4+4=3. So it would
// be better not to remove the negative number, and let 4 be the highest number achievable, without any sums
// -- (3,-1,4) in this case removing -1 will result in 3-1+4=6, 6 is bigger than both 3 and 4, so it would be convienent to remove the
// negative number and sum all of the three up into one number
///so what this step does is shrink the array furthermore if it is possible to 'remove' any negatives in a smart way
///i also make it reiterate for as long as there is no more shrinking available, because if you think about it not always
///can the pc know if, after a shrinking has occured, there are more shrinkings to be done
///then, lastly, it will calculate which of the positive numbers left is highest, and it will choose that as remaining maximum sum :)
///expected result for the array of input, s[], would be (i think), 7
int main() {
const int n=4;
int s[n+1]={3,-2,4,-4,6};
int k[n+1]={0};
///PRINT ARRAY, FOR DEBUG
std::cout<<" ( ";
for (int i = 0; i <= n; i++) { std::cout<<k[i]<<" "; }
std::cout<<")"<<std::endl;
int i=0, j=0;
// step 1: compress negative and postive subsegments of array s[] into single numbers within array k[]
/*while (i<=n)
{
while (s[i]>=0)
{
k[j]+=s[i]; ++i;
}
++j;
while (s[i]<0)
{
k[j]+=s[i]; ++i;
}
++j;
}*/
while (i<=n)
{
while (s[i]>=0)
{
if (i>n) break;
k[j]+=s[i]; ++i;
}
++j;
while (s[i]<0)
{
if (i>n) break;
k[j]+=s[i]; ++i;
}
++j;
}
std::cout<<"STEP 1 : ";
///PRINT ARRAY, FOR DEBUG
std::cout<<" ( ";
for (int i = 0; i <= n; i++) { std::cout<<k[i]<<" "; }
std::cout<<")"<<std::endl;
j=0;
// step 2: remove negative numbers when handy
std::cout<<"checked WRONG! "<<unsigned(k[3])<<std::endl;
int p=1;
while (p!=0)
{
p=0;
while (j<=n)
{
std::cout<<"checked right! "<<unsigned(k[j+1])<<std::endl;
if (k[j]<=0) { ++j; continue;}
if ( k[j]>unsigned(k[j+1]) && k[j+2]>unsigned(k[j+1]) )
{
std::cout<<"checked right!"<<std::endl;
k[j+2]=k[j]+k[j+1]+k[j+2];
k[j]=0; k[j+1]=0;
++p;
}
j+=2;
}
}
std::cout<<"STEP 2 : ";
///PRINT ARRAY, FOR DEBUG
std::cout<<" ( ";
for (int i = 0; i <= n; i++) { std::cout<<k[i]<<" "; }
std::cout<<")"<<std::endl;
j=0; i=0; //i will now use "i" and "p" variables for completely different purposes, as not to waste memory
// i will be final value that algorithm needed to find
// p will be a value to put within i if it is the biggest number found yet, it will keep changing as i go through the array....
// step 3: check which positive number is bigger: IT IS THE MAX ACHIEVABLE SUM!!
while (j<=n)
{
if(k[j]<=0) { ++j; continue; }
p=k[j]; if (p>i) { std::swap(p,i); }
j+=2;
}
std::cout<<std::endl<<"MAX ACHIEVABLE SUM WITHIN SUBSEGMENTS OF ARRAY : "<<i<<std::endl;
return 0;
}
might there be problems because im not using vectors??
Thanks for your help!
EDIT: i found both my algorithm bugs!
one is the one mentioned by user m24p, found in step 1 of the algorithm, which i fixed with a kinda-ugly get-around which ill get to cleaning up later...
the other is found in step2. it seems that in the while expression check, where i check something against unsigned values of the array, what is really checked is that something agains unsigned values of some weird numbers.
i tested it, with simple cout output:
IF i do unsigned(k[anyindexofk]) and the value contained in that spot is a positive number, i get the positive number of course which is unsigned
IF that number is negative though, the value won't be simply unsigned, but look very different, like i stepped over the array or something...i get this number "4294967292" when im instead expecting -2 to return as 2 or -4 to be 4.
(that number is for -4, -2 gives 4294967294)
I edited the sources with my new stuff, thanks for the help!
EDIT 2: nvm i resolved with std::abs() using cmath libs of c++
would there have been any other ways without using abs?

Answer 1

In your code, you have:
while (s[i]>=0)
{
k[j]+=s[i]; ++i;
}
Where s is initialized like so
int s[n+1]={3,-2,4,-4,6};
This is one obvious bug. Your while loop will overstep the array and hit garbage data that may or may not be zeroed out. Nothing stops i from being bigger than n+1. Clean up your code so that you don't overstep arrays, and then try debugging it. Also, your question is needs to be much more specific for me to feel comfortable answering your question, but fixing bugs like the one I pointed out should make it easier to stop running into inconsistent, undefined behavior and start focusing on your algorithm. I would love to answer the question but I just can't parse what you're specifically asking or what's going wrong.