C Level 6: Dynamic Heap Allocation (malloc/free)

## Stack vs Heap Memory Allocation

- **Stack**: Managed automatically by CPU call frames. Fast, but fixed size. Cleared on return.
- **Heap**: Managed manually by programmer via stdlib. Persists until explicitly freed.

### Heap Management Functions (`<stdlib.h>`)
- `malloc(bytes)`: Allocates uninitialized memory on Heap.
- `calloc(num, size)`: Allocates zero-initialized memory.
- `free(ptr)`: Releases heap block back to OS.

STACK vs HEAP MEMORY MODEL:
STACK: [ main() frame ] ──► ptr (pointer holding 0x9000)
                              │
HEAP:                         ▼
                            [ Allocated Heap Memory (0x9000) ]
                            (Persists until free(ptr) is called)

• Memory Leak: Calling malloc() without calling free() before program exits.
• Dangling Pointer: Accessing pointer memory after calling free(). Fix: set ptr = NULL.
• Missing NULL check after malloc allocation call.

#include <stdio.h>
#include <stdlib.h>

int main() {
    int *arr = (int*) malloc(5 * sizeof(int));
    if (arr == NULL) {
        printf("Allocation failed!\n");
        return 1;
    }
    arr[0] = 50;
    printf("Heap value: %d\n", arr[0]);
    free(arr); // MANDATORY
    arr = NULL; // Prevent dangling pointer
    return 0;
}

Checks for allocation NULL failure, uses dynamic memory, frees heap block, and nullifies pointer.

What happens if a program calls `malloc()` continuously in a loop without ever calling `free()`?