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Free

The free function deallocates memory that was previously allocated by malloc, calloc, or realloc.

int *ptr = malloc(4 * sizeof(int));
free(ptr);

IMPORTANT: free does not change the value stored in the memory, and it doesn't even change the address stored in the pointer. Instead, it simply informs the operating system that the memory can be used again.

Forgetting to free

Forgetting to call free leads to a memory leak. This means that the allocated memory remains occupied and cannot be reused, even though the program no longer needs it. Over time, if a program continues to allocate memory without freeing it, the program may run out of memory and crash.

Memory leaks are one of the most common bugs in C programs, and they can be difficult to track down because the memory is still allocated and accessible, even though it is no longer needed.

Assignment

We may be inefficient here at Sneklang, but we don't want outright memory leaks!

Run the code in its current state. After a number of successful allocations you should get a failure. The program is running out of memory due to a leak.

See how it's calling the allocate_scalar_list function in a loop? Well, the lists aren't needed from loop to loop, so they should be freed at the end of each iteration. If we do that, we should be able to allocate as many lists as we want (because we return the memory in between iterations).
Fix the code by freeing the allocated list at the end of each loop.