Segmentation fault when allocating large arrays on the stack

Question

When I compiled this simple C code it's fine but after uncommenting the line it shows segmentation fault. I don't know what's wrong with this. Please help.

#include<stdio.h>
int main()
    {
    int arr[10002][10002];
    int color[10002];
    int neigh;
 // scanf("%d",&neigh);
    return 0;
    }

Answer 1

You're blowing the stack with arr and color. Presumably when your call to scanf is commented out the compiler optimises all these variables away, but when it's present it attempts to allocate memory on the stack.

Make the variables global, and read up on stack memory vs heap memory.

#include<stdio.h>

int arr[10002][10002];
int color[10002];

int main()
{
    int neigh;
    scanf("%d",&neigh);
    return 0;
}

Answer 2

Variables allocated inside a function are put on the stack, which has a limited size. You can allocate them on the (larger) heap instead by using malloc.