Implement Stack Using Array

Use a fixed array and an integer top initialized to -1. For push, first check top + 1 < capacity; increment top and store the value. For pop, first check top is not -1; return the value at top and decrement it. Peek returns the current top value without changing top, and size is top + 1. The representation invariant is simple: valid elements occupy indices 0 through top, with no valid element outside that range. Decide and document what overflow and underflow return or throw, because many coding platforms prescribe -1 while production code may use exceptions or options. Test capacity zero if supported, one-element push/pop, popping after emptying, and pushing again after pop. Unlike a dynamic array, fixed-capacity push is strict O(1) but can fail when full. Every operation is O(1); storage is O(capacity).