Code Blocks doesn't show any error but still can't show output (0xC00000FD)

Question

I have this code:

#include <iostream>
#include <iomanip>

using namespace std;
main()
{
    int i, n, a[n], b[n], c[n];

    cout << "Program kreira nizove po matematickoj zavisnosti" << endl;
    cout << "Unesite vrednost n =" << endl;
    cin >> n;

    for (i = 0; i <=n; i++)
    {
        a[i] = (i+1)*2;

        if (i%2==0) b[i] = 2*i;
            else b[i] = -2*i;

        c[i] = a[i] - b[i];

    }
    cout << "A" << setw(3) << "B" << setw(3) << "C" << endl;
    cout << a[i] << setw(3) << b[i] << setw(3) << c[i] << endl;
}

And it shows me "Process returned -1073741571 (0xC00000FD)" Can't find what is problem. When I try other code, it works. Platform is Win 10.

`n` is not initialized before using it as the size of your arrays. — Fred Larson, Dec 08 '20 at 15:04
`int i, n, a[n], b[n], c[n];` what is the value of `n` when these non-standard arrays are allocated? Note that although `c` supports VLAs, officially `c++` does not: [https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard](https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard) — drescherjm, Dec 08 '20 at 15:04

score 1 · Answer 1 · answered Dec 08 '20 at 15:06

You are using a non-standard variable-length array (VLA) C++ extension, and you have stack overflow because n is not initialized before declaring arrays like a[n].

If you want to keep using VLA, need to move declaration int a[n], b[n], c[n]; below cin >> n;. Or use std::vector<int> instead.

score 1 · Accepted Answer · answered Dec 08 '20 at 15:06

1

This line:

int i, n, a[n], b[n], c[n];

has two problems:

Variable length arrays are non-standard, and:
n is uninitialised so a[n] tries to allocate an array of some indeterminate size on the stack. Which, in your case, is too large and is causing a stack overflow.

So, initialise n before you use it, and rather than using variable length arrays, use std::vector.

answered Dec 08 '20 at 15:06

Paul Sanders

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Ok, but I need to get message, so I can type in value of n. Do you know how I can do that? – Djordje Rankovic Dec 08 '20 at 15:10
You could put `int a[n], b[n], c[n];` after you ask the value of `n` – drescherjm Dec 08 '20 at 15:14
You have other bugs after that. `for (i = 0; i <=n; i++)` will cause an off by 1 error. remember that a[n] is out of bounds so when i == n you are accessing one element beyond the end of the arrays. – drescherjm Dec 08 '20 at 15:15
@drescherjm No, C++ does not have VLAs. Please do not recommend this. – Asteroids With Wings Dec 08 '20 at 15:38

score 0 · Answer 3 · answered Dec 08 '20 at 15:36

Achieved to find solution... Here is the final result:

#include <iostream>
#include <iomanip>
using namespace std;
main()
{
    int i, n, a[100], b[100], c[100];

    cout << "Program kreira nizove po matematickoj zavisnosti" << endl;
    cout << "Unesite vrednost n = ";
    cin >> n;
    cout << "A" << setw(10) << "B" << setw(10) << "C" << endl;

    for (i = 0; i <= n; i++)
    {
        a[i] = (i+1)*2;

        if (i%2==0) b[i] = 2*i;
            else b[i] = -2*i;

        c[i] = a[i] - b[i];

        cout << a[i] << setw(10) << b[i] << setw(10) << c[i] << endl;
    }
}

I changed value of array to something I'll never use (like 100) and I put cout in for loop, so it can type results one under other. It managed to work perfectly. Thank you for your help!

Using fixed-length arrays instead of vectors in a situation like this is a bad habit. Don't get used to it. You can get away with it in a toy example, but not in real software. — Eugene, Dec 08 '20 at 16:21

Code Blocks doesn't show any error but still can't show output (0xC00000FD)

3 Answers3