Stacks MCQ Practice Test

Q1. A stack-based function evaluator encounters the expression "2 3 + 5 *" (using postfix notation). Assuming the stack initially contains only the integer 1, what is the top element of the stack after the evaluation is complete?

• A. 17
• B. 25 ✓
• C. 16
• D. 11

Q2. A stack is used to keep track of function calls in a program. Imagine a scenario where functions A, B, and C are called sequentially, with B calling C. Which function's return will be processed "last" by the program, according to the Last-In, First-Out (LIFO) nature of the stack?

• A. Function A
• B. Function B
• C. Function C ✓
• D. The order doesn't matter with a stack

Q3. Consider a stack-based language interpreter where function calls are implemented using a stack to manage the function's activation records. Each activation record contains the function's local variables, return address, and arguments. A function 'foo' calls function 'bar', which in turn calls 'baz'. 'baz' returns to 'bar', which then returns to 'foo'. If a runtime error occurs within 'bar', causing an immediate program termination (without unwinding the stack properly), which of the following statements most accurately describes the state of the stack at the point of termination?

• A. The stack will contain only the activation record for 'bar'.
• B. The stack will contain the activation records for 'foo', 'bar', and 'baz', in that order (top to bottom).
• C. The stack will contain the activation records for 'foo' and 'bar', in that order (top to bottom). ✓
• D. The stack's state is unpredictable and may contain partial activation records.

Q4. A stack is implemented using a linked list. Each node contains an integer value and a reference to the next node. What is the correct way to implement the pop operation?

• A. Create a new node and copy the value of the current top node into it, then update the top reference to point to the new node.
• B. Update the value of the current top node with the value of the next node.
• C. Store the value of the current top node, update the top reference to point to the next node, and then return the stored value. ✓
• D. Delete the current top node and update the top reference to point to the node after the current top node.

Q5. A stack is implemented as a linked list with a pointer to the top element. When the stack is empty, the pointer points to a sentinel node with a value of -1. What is the purpose of this sentinel node?

• A. to indicate the end of the stack ✓
• B. to store the minimum element
• C. to simplify stack traversal
• D. to handle push and pop operations

Q6. In a stack implementation, what is the correct order of operations when a new element is pushed onto the stack and the top element is immediately popped?

• A. The new element is added at the beginning of the stack and the top element is removed first.
• B. The new element is added at the end of the stack and the top element is removed last.
• C. The new element is added at the end of the stack and the top element is removed first. ✓
• D. The new element is added at the beginning of the stack and the top element is removed last.

Q7. What are the contents of the stack after the following operations: push(5), push(3), pop(), push(7), pop()?

• A. The stack contains only the value 7 ✓
• B. The stack contains the values 5 and 7
• C. The stack is empty
• D. The stack contains only the value 3

Q8. Given a stack implementation with the following operations: push, pop, top, and isEmpty, which of the following is a correct implementation of the top operation?

• A. return stack[stack.length - 1]; ✓
• B. return stack[stack.length];
• C. return stack.pop();
• D. return stack.push()

Q9. A stack is implemented using a linked list. When a new element is pushed onto the stack, the linked list is inserted at the beginning. Which of the following correctly describes the order of elements in the linked list after the following sequence of operations: push(5), push(10), pop(), push(7)?

• A. The linked list is in the order: 5, 10, 7
• B. The linked list is in the order: 10, 7, 5
• C. The linked list is in the order: 5, 7, 10
• D. The linked list is in the order: 10, 5, 7 ✓

Q10. Given a stack implementation with the following push and pop operations, which of the following is the correct implementation of a function to check if an element is at the top of the stack without popping it?

• A. function isAtTop(stack, element) { while (stack.size() > 1) stack.pop(); return stack.contains(element); }
• B. function isAtTop(stack, element) { return stack.peek() == element; } ✓
• C. function isAtTop(stack, element) { stack.push(element); return true; }
• D. function isAtTop(stack, element) { stack.pop(); return stack.peek() == element; }

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