A queue is a container adaptor that provides a FIFO (First-In-First-Out) data structure. The standard library's std::queue is defined in the header <queue>.

Initialization

• Empty Queue:

std::queue<int> q;

Adding Elements

• Append to End:

q.push(4);

Access Elements

• Access Next Element:

int next = q.front();

• Access Last Element:

int last = q.back();

Removing Elements

• Remove Next Element:

q.pop();  // Removes the element at the front of the queue

Query Attributes

• Get Queue Size:

size_t size = q.size();

• Check if Queue is Empty:

bool isEmpty = q.empty();

Other Common Operations

• Swap Contents:

std::queue<int> q1, q2;
q1.swap(q2);  // Swaps the contents of q1 and q2

Examples

#include <iostream>
#include <queue>

int main() {
    std::queue<int> q;

    // Adding elements to the queue
    q.push(1);
    q.push(2);
    q.push(3);

    // Accessing elements
    std::cout << "Front: " << q.front() << std::endl; // Outputs 1
    std::cout << "Back: " << q.back() << std::endl;  // Outputs 3

    // Removing elements
    q.pop();  // Now the front is 2

    // Checking size and if empty
    std::cout << "Size: " << q.size() << std::endl; // Outputs 2
    std::cout << "Is empty: " << (q.empty() ? "Yes" : "No") << std::endl;  // Outputs No

    return 0;
}