代码适用于较小的输入，但不适用于大型输入。 为什么？

Question

Given a matrix of m * n elements (m rows, n columns), return all elements of the matrix in spiral order. Why is it working for smaller inputs but not for larger inputs? While this same code is working on other systems. The inputs and the outputs I used are given below.

#include<iostream>
using namespace std;
int main(){

    int n,m;
    cin>>n>>m;

    int a[n][m];

    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
            cin>>a[i][j];   
    }
    
    // spiral order print

    int row_start = 0, row_end = n-1, column_start = 0, column_end = m-1;
    while (row_start <= row_end && column_start <= column_end)
    {
        //for row start
        for (int col = column_start; col <= column_end; col++)
        {
            cout<<a[row_start][col]<<" ";
        }
        row_start++;

        //for column end
        for (int row = row_start; row <= row_end; row++)
        {
            cout<<a[row][column_end]<<" ";
        }
        column_end--;

        //for row end
        for (int col = column_end; col >= column_start; col--)
        {
            cout<<a[row_end][col]<<" ";
        }
        row_end--;

        //for column start
        for (int row = row_end; row >= row_start; row--)
        {
            cout<<a[row][column_start]<<" ";
        }
        column_start++;
    }
    
return 0;
}

INPUT:

5 6
1 5 7 9 10 11
6 10 12 13 20 21
9 25 29 30 32 41
15 55 59 63 68 70
40 70 79 81 95 105

OUTPUT:

1 5 7 9 10 1878030368 -1 -1 6422096 4200108 40 70 68 63 59 30 20 11 6 10 12 13 29 55 15 41 32 21 9 25 9

Answer 1

Check your code:

for (int i = 0; i < n; i++)
{
    for (int j = 0; j < n; j++)
        cin>>a[i][j];   
}

The second condition should be: j < m

My guess is your code is accessing garbage memory.