The following postfix expression with single digit operands is evaluated using…
200720252025202120122018
The following postfix expression with single digit operands is evaluated using a stack:
8 2 3 ^ / 2 3 * + 5 1 * - Note that ^ is the exponentiation operator. After the first * operator has been evaluated, the top two stack elements, listed from top to bottom, are:
Answer: A. 6, 1 — Concept: A postfix (Reverse Polish) expression is evaluated with one stack by scanning tokens from left to right. Each operand is pushed when encountered. For…
- A.
6, 1
- B.
5, 7
- C.
3, 2
- D.
1, 5
Attempted by 645 students.
Show answer & explanation
Correct answer: A
Concept: A postfix (Reverse Polish) expression is evaluated with one stack by scanning tokens from left to right. Each operand is pushed when encountered.
For a binary operator, pop the top value as b and the next value as a, compute a op b, and push the result. The order matters for subtraction, division, and exponentiation; the current stack after any token prefix is the complete evaluation state at that point.
Application: Process the expression only through the first multiplication, recording the stack from bottom to top after each token.
Push 8 → stack: [8]
Push 2 → stack: [8, 2]
Push 3 → stack: [8, 2, 3]
'^' pops b = 3 and a = 2, computes 2 cubed (23) = 8 → push 8 → stack: [8, 8]
'/' pops b = 8 and a = 8, computes a/b = 8/8 = 1 → push 1 → stack: [1]
Push 2 → stack: [1, 2]
Push 3 → stack: [1, 2, 3]
First '*' pops b = 3 and a = 2, computes a×b = 2×3 = 6 → push 6 → stack: [1, 6]
Result: The stack is [1, 6] from bottom to top, so its top two values listed from top to bottom are 6, 1.
Cross-check: Pair each postfix operator with its two preceding operands to obtain ((8 / 2 cubed) + (2×3)) − (5×1). Direct evaluation gives (8/8 + 6) − 5 = (1 + 6) − 5 = 2. The two subexpressions completed before '+' are 8/2 cubed = 1 and 2×3 = 6, independently confirming that immediately after the first '*' the stack is [1, 6] from bottom to top.
A video solution is available for this question — log in and enroll to watch it.
Explore the full course: Iocl Engineers Officers Grade A Paper 2