# deque::push_front() in C++ STL

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In this article we will be discussing the working, syntax and examples of deque::push_front() function in C++ STL.

## What is Deque?

Deque is the Double Ended Queues that are the sequence containers which provides the functionality of expansion and contraction on both the ends. A queue data structure allow user to insert data only at the END and delete data from the FRONT. Let’s take the analogy of queues at bus stops where the person can be inserted to a queue from the END only and the person standing in the FRONT is the first to be removed whereas in Double ended queue the insertion and deletion of data is possible at both the ends.

## What is deque::push_front()?

deque::push_front() is an inbuilt function in C++ STL which is declared in header file. deque::push_front() is used to push/insert an element at the front or at the beginning of the deque container making the pushed/inserted element as the first element of the deque. This function accepts one argument, that is, the element which is to be pushed/inserted at the beginning.

## Syntax

mydeque.push_front(const value_type& value);
This function accepts one parameter which is the element which is to be inserted

## Return value

This function returns nothing.

## Example

Input: deque<int> mydeque = {10, 20 30, 40};
mydeque.push_front(9);
Output:
Deque elements: 9 10 20 30 40
Input: deque<int> mydeque;
mydeque.push_front(5);
Output: 5

## Example

Live Demo

#include <deque>
#include <iostream>
using namespace std;
int main(){
deque<int> Deque = { 20, 30, 40, 50 };
Deque.push_front(10);
cout<<"Elements in Deque are : ";
for(auto i = Deque.begin(); i!= Deque.end(); ++i)
cout << ' ' << *i;
}

## Output

If we run the above code it will generate the following output −

Elements in Deque are : 10 20 30 40 50

## Example

Live Demo

#include <deque>
#include <iostream>
using namespace std;
int main(){
int total = 0;
deque<int> Deque;
Deque.push_front(10);
Deque.push_front(20);
Deque.push_front(30);
Deque.push_front(40);
while (!Deque.empty()){
total++;
Deque.pop_front();
}
cout<<"Total number of elements in a deque are : "<<total;
return 0;
}

## Output

If we run the above code it will generate the following output −

Total number of elements in a deque are : 4
Published on 05-Mar-2020 15:39:07