Difference between array type and array allocated with malloc

There are several different pieces at play here.

The first is the difference between declaring an array as

int array[n];

and

int* array = malloc(n * sizeof(int));

In the first version, you are declaring an object with automatic storage duration. This means that the array lives only as long as the function that calls it exists. In the second version, you are getting memory with dynamic storage duration, which means that it will exist until it is explicitly deallocated with free.

The reason that the second version works here is an implementation detail of how C is usually compiled. Typically, C memory is split into several regions, including the stack (for function calls and local variables) and the heap (for malloced objects). The stack typically has a much smaller size than the heap; usually it's something like 8MB. As a result, if you try to allocate a huge array with

int array[n];

Then you might exceed the stack's storage space, causing the segfault. On the other hand, the heap usually has a huge size (say, as much space as is free on the system), and so mallocing a large object won't cause an out-of-memory error.

In general, be careful with variable-length arrays in C. They can easily exceed stack size. Prefer malloc unless you know the size is small or that you really only do want the array for a short period of time.

Hope this helps!

int list[n]

Allocates space for n integers on the stack, which is usually pretty small. Using memory on the stack is much faster than the alternative, but it is quite small and it is easy to overflow the stack (i.e. allocate too much memory) if you do things like allocate huge arrays or do recursion too deeply. You do not have to manually deallocate memory allocated this way, it is done by the compiler when the array goes out of scope.

malloc on the other hand allocates space in the heap, which is usually very large compared to the stack. You will have to allocate a much larger amount of memory on the heap to exhaust it, but it is a lot slower to allocate memory on the heap than it is on the stack, and you must deallocate it manually via free when you are done using it.

int list[n] stores the data in the stack, while malloc stores it in the heap.

The stack is limited, and there is not much space, while the heap is much much bigger.