ITPEC FE Morning October 2019 Question 6

Stack operations — trace PUSH/POP sequence to find final stack state.

Execute operations on an initially empty stack:

• •PUSH 1 → [1]
• •PUSH 5 → [1, 5]
• •POP → removes 5 → [1]
• •PUSH 7 → [1, 7]
• •PUSH 6 → [1, 7, 6]
• •PUSH 4 → [1, 7, 6, 4]
• •POP → removes 4 → [1, 7, 6]
• •POP → removes 6 → [1, 7]
• •PUSH 3 → [1, 7, 3]

Final stack (top to bottom): 3, 7, 1 → (c)

Why not others:
- (a) 1, 7, 3 — wrong order (bottom-to-top instead of top-to-bottom)
- (b) 3, 4, 6 — implies 4 and 6 were never popped
- (d) 6, 4, 3 — implies 6 and 4 remained after the two POPs

Key rule: Stack is LIFO — POP always removes the most recently pushed element.

AI-generated — may contain errors