ITPEC FE Subject B October 2025 Question 8

Stack uses array stck[1..10] with tos as top-of-stack pointer, initially 0 (empty).

Push logic:
- Check overflow: tos = 10 → full
- A: tos ← tos + 1 (move pointer up first)
- Then stck[tos] ← item (store at new top)

Pop logic:
- Check underflow: tos < 1 → empty
- B: item ← stck[tos] (read current top), then tos ← tos - 1 (move pointer down)
- Return item

Why not others:
- a) — Pop increments tos (tos + 1) instead of decrementing — wrong direction
- c), d) — Pop section has wrong order or direction for tos
- e)–h) — Push decrements tos, but since tos starts at 0 and array starts at 1, push must increment

Key rule: When tos points to the current top element (not the next free slot), push increments before writing, pop reads before decrementing.

AI-generated — may contain errors