Queue vs Stack: What's the Difference?

The main difference between a queue and a stack lies in the order in which elements are added and removed:

• In a queue, elements follow the First-In-First-Out (FIFO) principle. The first element added to the queue will be the first one to be removed. Queues are often compared to a line of people waiting for a service, where the person who joins the line first gets served first.
• In a stack, elements follow the Last-In-First-Out (LIFO) principle. The last element added to the stack will be the first one to be removed. Stacks are often compared to a stack of plates, where the last plate placed on top of the stack is the first one to be removed.

In C++, the standard library provides the std::queue class template for queues and the std::stack class template for stacks. Both are container adaptors, meaning they use an underlying container to store the elements.

Here's an example illustrating the difference between a queue and a stack:

1#include <iostream>
2#include <queue>
3#include <stack>
4
5int main() {
6  std::queue<int> myQueue;
7  myQueue.push(1);
8  myQueue.push(2);
9  myQueue.push(3);
10
11  std::stack<int> myStack;
12  myStack.push(1);
13  myStack.push(2);
14  myStack.push(3);
15
16  // Output: 1
17  std::cout << "Queue front: "
18    << myQueue.front() << std::endl;
19
20  // Output: 3
21  std::cout << "Stack top: "
22    << myStack.top() << std::endl;
23}

1Queue front: 1
2Stack top: 3

In this example, the first element added to the queue (1) is the first one to be accessed using myQueue.front(), while the last element added to the stack (3) is the first one to be accessed using myStack.top().