Most of the time you don't build a stack — your language already has one. This lesson shows the built-in stack in each language, the mistakes people make with them, and then how to build your own stack on a linked list so you know exactly what happens underneath.
![A cheat sheet of stack operations in four languages. JavaScript arrays: push, pop, s[s.length - 1] to peek, length to check empty and size. Python lists: append, pop, s[-1], not s, len(s). Java ArrayDeque: push, pop, peek, isEmpty, size. C++ std::stack: push, pop which returns nothing, top, empty, size.](/drawings/15619ab3-7f14-4f16-a296-3c3a8f9aff15.svg)
Here is the same small job in all four: push some values, then pop until the stack is empty. The values come out reversed.
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