Stacks - General Questions

Evaluate the postfix expression: 5 2 4 * +

Starting with an empty stack, these operations are performed: push(9), pop(), push(7), pop(), push(8), push(8), pop(). What is at the top of the stack now?

Starting with an empty stack, these operations are performed: push(7), pop(), push(4), push(4), push(7), push(1), push(7). What is at the top of the stack now?

Convert the infix expression (A+B*C)*D to postfix.

Evaluate the postfix expression: 7 5 * 2 1 * -