Standard arrays in C++ are fixed-size containers allocated either on the stack or heap, storing elements contiguously in memory with zero-based indexing. Stack-allocated arrays offer automatic management and faster access, while heap-allocated ones provide dynamic sizing at runtime but require manual deallocation to avoid leaks. Knowing array sizes involves compile-time constants for stack arrays and runtime checks for dynamic ones.​

Stack Allocation
Stack arrays use fixed-size declarations like int arr[10];, where size must be known at compile-time. Memory allocates automatically upon entering scope and deallocates on exit, making them efficient and exception-safe. They suit small, predictable sizes but risk stack overflow for large arrays.​

Heap Allocation
Heap arrays use new like int* arr = new int[size];, enabling runtime size determination. Developers must pair with delete[] arr; for cleanup, as failure causes memory leaks; access remains fast due to contiguity. Prefer for large or variable-sized data, unlike std::vector which automates this.​

Size Concepts
Use sizeof(arr) / sizeof(arr[0]) for stack arrays to compute element count at compile-time, yielding 10 for int arr[10]. Heap arrays lack this; track size manually or use std::size() in C++17+ for std::array. Pointer decay prevents sizeof on decayed names, so store dimensions separately.​