What is the difference between a stack and a heap?

The main difference between a stack and a heap lies in their respective data structures and memory allocation methods.

1. Data Structure:
- Stack: A stack is a linear data structure that follows the Last-In-First-Out (LIFO) principle. It can be visualized as a stack of plates, where the last plate added is the first one to be removed.
- Heap: A heap is a binary tree-based data structure that follows a specific ordering property. It can be visualized as a complete binary tree, where each node has a value greater than or equal to its child nodes (in a max heap) or less than or equal to its child nodes (in a min heap).

2. Memory Allocation:
- Stack: Memory allocation in a stack is done automatically and in a fixed order. It uses a region of memory known as the stack frame, which is managed by the compiler. Memory is allocated and deallocated in a Last-In-First-Out manner, meaning the most recently allocated memory is the first to be deallocated.
- Heap: Memory allocation in a heap is dynamic and can be controlled manually. It uses a region of memory known as the heap, which is managed by the programmer. Memory is allocated and deallocated in any order, and the programmer is responsible for managing the memory allocation and deallocation.

3. Usage:
- Stack: Stacks are commonly used for function calls and local variables. When a function is called, its local variables and function call information are stored in the stack frame. Once the function execution is completed, the stack frame is removed, and the memory is freed.
- Heap: Heaps are used for dynamic memory allocation, such as creating objects or data structures that need to persist beyond the scope of a function. Memory allocated in the heap needs to be explicitly deallocated by the programmer to avoid memory leaks.

4. Memory Management:
- Stack: Memory management in a stack is automatic and handled by the compiler. The size of the stack is limited, and exceeding this limit can result in a stack overflow error.
- Heap: Memory management in a heap is manual and controlled by the programmer. The size of the heap is typically larger than the stack, but it can be limited by the available system memory. Improper memory management in the heap can lead to memory fragmentation or memory leaks.

In summary, the stack and heap differ in their data structures, memory allocation methods, usage, and memory management. The stack is a LIFO data structure with automatic memory allocation, primarily used for function calls and local variables. On the other hand, the heap is a binary tree-based data structure with dynamic memory allocation, used for creating objects or data structures that need to persist beyond the scope of a function.