C++: What is the difference between std::stack and std::queue?

stack — LIFO. queue — FIFO.

std::stack:

• Last in, first out.
• push() — add to top.
• pop() — remove from top.

1std::stack<int> s;
2s.push(1);
3s.push(2);
4s.push(3);
5std::cout << s.top();  // 3 (last in)

std::queue:

• First in, first out.
• push() — add to back.
• pop() — remove from front.

1std::queue<int> q;
2q.push(1);
3q.push(2);
4q.push(3);
5std::cout << q.front();  // 1 (first in)

Use cases:

• stack — undo, DFS, parentheses matching.
• queue — BFS, task scheduling, buffering.