When to use std::stack vs std::vector?

While std::stack and std::vector can both be used to store a collection of elements, they are designed for different use cases.

You would choose std::stack when:

• You need to enforce LIFO (last-in, first-out) access. A stack ensures elements can only be added and removed from one end.
• You only need access to the top element. If you don't need random access to elements, a stack provides a simpler interface.
• You want to prevent unintended access. The restricted interface of stack helps prevent bugs from accessing elements incorrectly.

You would choose std::vector when:

• You need random access to elements using an index. A vector allows accessing any element by its position.
• You need to iterate over elements. Vectors can be easily iterated using a range-for loop or iterators.
• You need the last element. While a stack can only access the top element, with a vector you can use back() to get the last element.

Here's an example showing cases where stack and vector are appropriate:

1#include <iostream>
2#include <stack>
3#include <vector>
4
5int main() {
6  // Use a stack when LIFO access is needed
7  std::stack<int> s;
8  s.push(1);
9  s.push(2);
10  s.push(3);
11  while (!s.empty()) {
12    std::cout << s.top() << ' ';  // prints 3 2 1
13    s.pop();
14  }
15
16  // Use a vector when random access is needed
17  std::vector<int> v{1, 2, 3};
18  std::cout << '\n' << v[1] << '\n';  // prints 2
19  for (int i : v) {
20    std::cout << i << ' ';  // prints 1 2 3
21  }
22}

13 2 1
22
31 2 3

So in summary - use std::stack for LIFO access to the top element only, and std::vector for random access, iteration, or access to the last element. The best choice depends on your specific access and usage requirements.