Stl Queue

• push(val): Adds element to back.
• pop(): Removes front element.
• front(): Returns front element.
• back(): Returns back element.

queue<int> q;
q.push(10); q.push(20);

cout << q.front(); // 10
q.pop();
cout << q.front(); // 20

Used in Breadth-First Search (BFS), task scheduling, printer spooling, and handling asynchronous data streams.