DSA · Theory

Stack Pointer

Theory

641/810

Stack Pointer is simple if you keep it on paper. Amit uses it for undo typing in a tiny editor.

Stack Pointer on the board — push / pop LIFO. Then say what undo typing looks like after.

Without Stack Pointer, a tiny editor gets messy and undo typing is hard to trust.

Use Stack Pointer when undo typing must stay clear. If a simpler DSA step works, use that instead.

Stack Pointer trap — pop on empty. Amit loses marks for that every viva.

Stack Pointer is not a lonely heading. Amit ties it to undo typing.

Viva for Stack Pointer — what it is → push / pop LIFO → the mistake (pop on empty).

Diagram

    | 3 |  ← top (pop)
    | 2 |
    | 1 |
    LIFO

Exam tip

For Stack Pointer: definition + a tiny editor + one failure.

stack = []
stack.append(10)   # push
stack.append(20)
print(stack.pop()) # 20
print(stack[-1])   # peek → 10

Stack Pointer — stack is LIFO: push/pop from the same end.