What do Push and Pop mean for Stacks?

Question

long story short my lecturer is crap, and was showing us infix to prefix stacks via an overhead projector and his bigass shadow was blocking everything so i missed the important stuff

he was referring to push and pop, push = 0 pop = x

he gave an example but i cant see how he gets his answer at all,

2*3/(2-1)+5*(4-1)

step 1 Reverse : )1-4(*5+)1-2(/3*2 ok i can see that

he then went on writing x's and o's operations and i got totally lost

answer 14-5*12-32*/+ then reversed again to get +/*23-21*5-41

if some one could explain to me the push pop so i could understand i would be very greatful, i have looked online but alot stuff im finding seems to be a step above this, so i really need to get an understanding here first

Answer 1

Hopefully this will help you visualize a Stack, and how it works.

Empty Stack:

|     |
|     |
|     |
-------

After Pushing A, you get:

|     |
|     |
|  A  |
-------

After Pushing B, you get:

|     |
|  B  |
|  A  |
-------

After Popping, you get:

|     |
|     |
|  A  |
-------

After Pushing C, you get:

|     |
|  C  |
|  A  |
-------

After Popping, you get:

|     |
|     |
|  A  |
-------

After Popping, you get:

|     |
|     |
|     |
-------