deque::empty() and deque::size() in C++ STL

In this article we will be discussing the working, syntax and examples of deque::empty() and deque::size() functions 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::empty()?

deque::empty() is an inbuilt function in C++ STL which is declared in <deque> header file. deque::empty() checks whether the given deque container is empty(size is 0) or not, and returns true value if the container associated with the function is empty and false if the container is not empty.

Syntax

mydeque.empty();

Parameter

This function accepts no parameter

Return value

This function returns true if the given deque container is empty or the size of the deque container is 0, else the function returns false if there are some elements in the deque associated with the function or the size of the container is not zero.

Example

Input: deque<int> mydeque = {10, 20 30, 40};
      mydeque.empty();
Output:
      False
Input: deque<int> mydeque;
      mydeque.empty();
Output: True

Example

Live Demo

#include <deque>
#include <iostream>
using namespace std;
int main(){
   int product = 1;
   deque<int> Deque;
   //inserting elements to a deque using push_back() function
   Deque.push_back(10);
   Deque.push_back(20);
   Deque.push_back(30);
   Deque.push_back(40);
   Deque.push_back(50);
   //traversing deque while it willn’t gets empty using empty() function
   while(!Deque.empty()){
      product = product * Deque.front();
      Deque.pop_front();
   }
   //check if deque is empty or not
   if(Deque.empty()){
      cout<<"Deque is empty and hence product is : "<<product;
   } else {
      cout<<"Deque is not empty ";
   }
   return 0;
}

Output

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

Deque is empty and hence product is : 12000

What is deque::size()?

deque::size() is an inbuilt function in C++ STL which is declared in header file. deque::size() returns the size of the deque container associated with the function. If the container has no elements then the function returns 0.

Syntax

mydeque.size();

Parameter

This function accepts no parameter

Return value

This function returns an unsigned integer value i.e., the number of elements present in the container.

Example

Input: deque<int> mydeque = {10, 20 30, 40};
   mydeque.size();
Output:
   4
Input: deque<int> mydeque;
   mydeque.size();
Output: 0

Example

Live Demo

#include <deque>
#include <iostream>
using namespace std;
int main(){
   int product = 0;
   deque<int> Deque;
   //inserting elements to a deque
   Deque.push_back(10);
   Deque.push_back(20);
   Deque.push_back(30);
   Deque.push_back(40);
   Deque.push_back(50);
   //checking the size of a deque
   cout<<"size of deque is : "<<Deque.size();
   return 0;
}