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Check if a queue is empty or not using queue::size() function

Check queue is empty or not in C++ STL: Here, we are going to learn check whether a given queue is an empty queue or not using C++ STL?
Submitted by IncludeHelp, on November 27, 2018

There is a function queue::empty() that can be used to check whether queue is empty or not – it returns 1 (true) if queue is empty else returns 0 (false).

But, in this example – we are checking it by using queue::size() function.

If we don't want to use queue::empty() function, we can check the size of the queue, if it is 0 – queue is an empty queue, if it is not 0 (greatest than zero), queue is empty.

Program:

#include <iostream>
#include <queue>
using namespace std;

//Main fubction
int main() 
{
	// declaring two queues
	queue<int> Q1;
	queue<int> Q2;

	//inserting elements to Q1
	Q1.push(10);
	Q1.push(20);
	Q1.push(30);

	if(Q1.size()==0)
		cout<<"Q1 is an empty queue"<<endl;
	else
		cout<<"Q1 is not an empty queue"<<endl;

	if(Q2.size()==0)
		cout<<"Q2 is an empty queue"<<endl;
	else
		cout<<"Q2 is not an empty queue"<<endl;

	return 0;
}

Output

Q1 is not an empty queue 
Q2 is an empty queue