Stacks and queues are data structures that store elements of a specific data type. They have various operations (methods/functions) to input, output and manage the data.
Stack implements a last-in, first-out (LIFO) policy on its elements. So, the element removed from the stack is always the most recently inserted one. On the other hand, Queue implements first-in, first-out (FIFO) policy on its elements. Hence in a queue, the deleted element is always the element that has been inserted for the longest time.
Stack
These are the operations provided for a stack:
Stack-Empty (S) 1. if S.empty() == true 2. return true 3. else 4. return false Push (S, x) 1. S.size() = S.size() + 1 2. S.push(x) Pop (S) 1. if Stack-Empty (S) 2. return NULL 3 else 4. x = S.top() 5 S.size() = S.size() - 1 6. S.pop() 7. return x
Code Implementation
//
// main.cpp
// Stack
//
// Created by Himanshu on 03/10/21.
//
#include <iostream>
#include <stack>
using namespace std;
int main () {
stack<int> st;
cout<<"Push(x) {10, 20, 30, 40, 50}"<<endl;
st.push(10);
st.push(20);
st.push(30);
st.push(40);
st.push(50);
cout<<"Stack-Empty(): ";
if (st.empty()) {
cout<<"Stack is empty"<<endl;
} else {
cout<<"Stack is not empty"<<endl;
}
cout<<"Pop elements..."<<endl;
while (!st.empty()) {
cout<< st.top()<<" ";
st.pop();
}
cout<<endl;
cout<<"Stack-Empty(): ";
if (st.empty()) {
cout<<"Stack is empty"<<endl;
} else {
cout<<"Stack is not empty"<<endl;
}
return 0;
}
Output
Push(x) {10, 20, 30, 40, 50}
Stack-Empty(): Stack is not empty
Pop elements...
50 40 30 20 10
Stack-Empty(): Stack is empty
Here’s a working example: C++ STL Stack
Queue
These are the operations provided for a queue:
Queue-Empty (Q) 1. if Q.empty() == true 2. return true 3. else 4. return false Enqueue (Q, x) 1. Q.size() = Q.size() + 1 2. Q.push(x) Dequeue (Q) 1. if Queue-Empty (Q) 2. return NULL 3 else 4. x = Q.front() 5 Q.size() = Q.size() - 1 6. Q.pop() 7. return x
Code Implementation
//
// main.cpp
// Queue
//
// Created by Himanshu on 03/10/21.
//
#include <iostream>
#include <queue>
using namespace std;
int main () {
queue<int> qu;
cout<<"Enqueue(x) {10, 20, 30, 40, 50}"<<endl;
qu.push(10);
qu.push(20);
qu.push(30);
qu.push(40);
qu.push(50);
cout<<"Queue-Empty(): ";
if (qu.empty()) {
cout<<"Queue is empty"<<endl;
} else {
cout<<"Queue is not empty"<<endl;
}
cout<<"Dequeue elements..."<<endl;
while (!qu.empty()) {
cout<<qu.front()<<" ";
qu.pop();
}
cout<<endl;
cout<<"Queue-Empty(): ";
if (qu.empty()) {
cout<<"Queue is empty"<<endl;
} else {
cout<<"Queue is not empty"<<endl;
}
return 0;
}
Output
Enqueue(x) {10, 20, 30, 40, 50}
Queue-Empty(): Queue is not empty
Dequeue elements...
10 20 30 40 50
Queue-Empty(): Queue is empty
Here’s a working example: C++ STL Queue