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I challenge you to find what the heck is causing my program to break, I've been trying to find a reasoning behind this but I haven't been able to find even the slightest bit.

My program is supposed to read values from a file and depending on what it reads create 2 matrix: first value on the file is rows and second one cols. (Then it's supposed to do some algorithms but that works just fine, it's failing before that)

So here's my problem: I keep getting the following error message when running the program only when the rows value is 30. I haven't been able to find a single value that makes this fail other than 30. I want to fix this but I can't find what's causing the program to fail to begin with, I don't know what else to try. I debugged it and the program fails when creating the first matrix after reading all the info from the file.

    potter: malloc.c:2401: sysmalloc: Assertion `(old_top == initial_top (av) && old_size == 0) || ((unsigned long) (old_size) >= MINSIZE && prev_inuse (old_top) && ((unsigned long) old_end & (pagesize - 1)) == 0)' failed.
Aborted (core dumped)
The funniest thing is the program was working just fine before adding the last function. I must have changed something without noticing and broken the program (I don't have any older versions and removing the function doesn't help)
Here's a link to the hole code and test files if anyone is interested: https://drive.google.com/open?id=1tcKXainj021fwjAAGN3cNdsU50p2Neou
Edit: The program fails in the following part of the code
M=new int * [n+1]                  
        if(M){                             
                for(int i=0; i<=n;i++){       
                        M[i]=new int [T+1];   
                        if(!M[i]){       
                                cerr<<"Error";
                                exit(-1);
                for(int i=0;i<n+1;i++)
                        for(int j=0;j<T+1;j++)
                                M[i][j]=-1;
        }else{
                cerr<<"Error";
                exit(-1);
Concretely when trying to do M[i]=new int [T+1]; when i=10 only if n=30
Solved
The problem was a loop going outside of allocated memory beforehand corrupting it and causing the program to fail later.
 decisions=new int [n];
                for(int i=0;i<=n;i++)
                        decisions[i]=0;
Honestly I don't know how the program didn't fail more having done something like this. (This was easily solved by changing n to n+1 in decisions=new int [n+1];)
                Please read the help pages, take the SO tour, read about how to ask good questions, as well as this question checklist. And don't forget to create a Minimal, Complete, and Verifiable Example to show us in the question. Questions should be self-contained. Lastly please learn how to debug your programs.
– Some programmer dude
                Nov 16, 2018 at 1:12
                As for possible reasons for the crash, it's typically happens when you have undefined behavior. More specifically it's very probable that you write out of bounds of allocated memory.
– Some programmer dude
                Nov 16, 2018 at 1:13
                But it fails when allocating, and only when trying to create a 30*X matrix, with anything bigger or smaller it works just fine
– Pau
                Nov 16, 2018 at 1:16
                if(M){  -- Unless you used nothrow, what compiler are you using where new [] returns nullptr if there is an error?  Actually new throws a std::bad_alloc exception when an error is encountered, and does not return 0, NULL, nullptr etc.  Thus this test and any others that test the return value of new[] are not necessary.
– PaulMcKenzie
                Nov 16, 2018 at 1:26
                I challenge you to find what the heck is causing my program to break -- Come on now --decisions=new int [n];for(int i=0;i<=n;i++)		decisions[i]=0; -- See anything wrong with that loop?  Also, you should post code here, not on an external web site that could be gone at any time, thus rendering this question worthless to anyone linking to it.
– PaulMcKenzie
                Nov 16, 2018 at 1:29
It's very probable that you've done something that corrupted the malloc data structure. This could be by reusing a freed pointer, overrunning the data you allocated (and thereby mashing the little header malloc uses) or accidentally freeing a pointer that doesn't point to the head of malloc-ed data.
There is a lovely tool called valgrind which is very helpful for this sort of thing.
                Thank you! Could you give me any tips in what should I do to find what's causing the corruption in the program? I have never used nemiver before and I would really find that helpful to be able to start somewhere
– Pau
                Nov 16, 2018 at 1:34
                @Pau Didn't you see my comment?  You are going out-of-bounds accessing the memory in your loop.
– PaulMcKenzie
                Nov 16, 2018 at 1:35
        
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