1 Stack Data : a collection of homogeneous elements arranged in a sequence. Only the first element may be accessed Main Operations: Push : insert an element at the top of the stack Pop : remove the top element This function does NOT return the top element (because if the stack were empty, the function would be undefined). Top : return the top element (without removing it) IsEmpty : return true is empty, false otherwise

2 Stack Main characteristics : LIFO structure: last in, first out Only the top element may be accessed at any time The only way to access an element in the middle of the stack is by popping all the elements above it.

3 Stack Stacks in the STL: #include There are no iterators (since it is not possible to traverse a stack). stack S; S.push(10); S.push(15); int x = S.top(); if (!S.empty()) S.pop();

4 Queue Data : a collection of homogeneous elements arranged in a sequence. Elements can inserted only at the back and removed only from the front. Operations: Enqueue : insert an element at the back Dequeue : remove an element from the front Front : return the front element IsEmpty : return true if empty, false otherwise.

5 Queue Main characteristics : FIFO structure: first in, first out Only the front element may be accessed at any time The only way to access an element in the middle of the queue is by removing all the elements before it.

6 Queue Implementing our own queue: Idea 1: Use contiguous memory (an array) Make the array circular. Idea 2: Use linked memory Use a node structure to store the data and a pointer to the next node: create a chain of nodes Which end of the list is the front of the queue? The head, since it can be deleted faster than the tail

7 Queue Queues in the STL #include no iterators queue Q; Q.push(10.45); Q.push(-6.78); int s = Q.size(); cout << Q.front() << endl; if (!Q.empty()) Q.pop();