# Nov 13, 2018

## Stack / Queue in C++ STL

### Stack

The functions associated with stack are:

[`empty()`](https://www.geeksforgeeks.org/stack-empty-and-stack-size-in-c-stl/) – Returns whether the stack is empty – Time Complexity : `O(1)`\
[`size()`](https://www.geeksforgeeks.org/stack-empty-and-stack-size-in-c-stl/) – Returns the size of the stack – Time Complexity : `O(1)`\
[`top()`](https://www.geeksforgeeks.org/stack-top-c-stl/) – Returns a reference to the top most element of the stack – Time Complexity : `O(1)`\
[`push(g)`](https://www.geeksforgeeks.org/stack-push-and-pop-in-c-stl/) – Adds the element `g` at the top of the stack – Time Complexity : `O(1)`\
[`pop()`](https://www.geeksforgeeks.org/stack-push-and-pop-in-c-stl/) – Deletes the top most element of the stack – Time Complexity : `O(1)`

```cpp
// CPP program to demonstrate working of STL stack 
#include <iostream> 
#include <stack> 
using namespace std; 
  
void showstack(stack <int> s) 
{ 
    while (!s.empty()) 
    { 
        cout << '\t' << s.top(); 
        s.pop(); 
    } 
    cout << '\n'; 
} 
  
int main () 
{ 
    stack <int> s; 
    s.push(10); 
    s.push(30); 
    s.push(20); 
    s.push(5); 
    s.push(1); 
  
    cout << "The stack is : "; 
    showstack(s); 
  
    cout << "\ns.size() : " << s.size(); 
    cout << "\ns.top() : " << s.top(); 
  
  
    cout << "\ns.pop() : "; 
    s.pop(); 
    showstack(s); 
  
    return 0; 
}
```

**Output:**

```
The stack is :     1    5    20    30    10

s.size() : 5
s.top() : 1
s.pop() :     5    20    30    10
```

### Queue

Queues are a type of container adaptors which operate in a first in first out (FIFO) type of arrangement. Elements are inserted at the back (end) and are deleted from the front.

**The functions supported by queue are :**

1. `empty()` – Returns whether the queue is empty
2. `size()` – Returns the size of the queue
3. `front()` – Returns a reference to the first element of the queue
4. `back()` – Returns a reference to the last element of the queue
5. `push(g)` – Adds the element `g` at the end of the queue
6. `pop()` – Deletes the first element of the queue

```cpp
// CPP code to illustrat
// Queue in Standard Template Library (STL)
#include <iostream>
#include <queue>
  
using namespace std;
  
void showq(queue <int> gq)
{
    queue <int> g = gq;
    while (!g.empty())
    {
        cout << '\t' << g.front();
        g.pop();
    }
    cout << '\n';
}

int main()
{
    queue <int> gquiz;
    gquiz.push(10);
    gquiz.push(20);
    gquiz.push(30);
  
    cout << "The queue gquiz is : ";
    showq(gquiz);

    cout << "\ngquiz.size() : " << gquiz.size();
    cout << "\ngquiz.front() : " << gquiz.front();
    cout << "\ngquiz.back() : " << gquiz.back();

    cout << "\ngquiz.pop() : ";
    gquiz.pop();
    showq(gquiz);

    return 0;
}
```

**Output:**

```
The queue gquiz is :     10    20    30

gquiz.size() : 3
gquiz.front() : 10
gquiz.back() : 30
gquiz.pop() :     20    30
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://lintcode-solutions.gitbook.io/project/oj-review/nov-13-2018.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.