Create a stack
Updated
A stack is a pile of values with one open end. Creating one means starting with no items and agreeing that every later change happens only at the top.
What to focus on
We write a = [bottom, …, top]. The last slot is the top. Empty is []. After creation there is no legal pop or peek until you push.
Worked examples
empty
no values- allocate an empty stack
- there is no top
Result: [] · size 0
one value
place 7 as the only item- bottom and top are both 7
Result: [7] · top 7
three values
place 4, then 1, then 9- 4 is bottom
- 9 is top
Result: [4, 1, 9] · top 9
Try it
Write create(values). values is a list of integers to push left to right. The last value becomes the top. Push each value in order. Print size and top. Empty has no top. On [] size is 0. On [7] size is 1 and top is 7. On [4, 1, 9] size is 3 and top is 9.
values is a list of integers. You may create an empty stack.