queue::empty() and queue::size() in C++ STL
Last Updated :
04 Jun, 2023
Queue is a type of container adaptor that operate in a first in first out (FIFO) type of arrangement. Elements are inserted at the back (end) and are deleted from the front.
queue::empty()
empty() function is used to check if the queue container is empty or not.
Syntax
queueName.empty()
Parameters
- This function does not accept any parameter.
Return Value
- It returns True if the list is empty, else it returns False.
Examples
Input: myqueue = 1, 2, 3
myqueue.empty();
Output: False
Input: myqueue
myqueue.empty();
Output: True
Errors and Exceptions
- Shows an error if a parameter is passed.
- Shows no exception throw guarantee.
Examples of queue::empty()
Example 1
The below C++ demonstrates the use of the empty() function in C++ STL’s queue class.
C++
#include <iostream>
#include <queue>
using namespace std;
int main()
{
queue< int > myqueue;
myqueue.push(1);
if (myqueue.empty()) {
cout << "True" ;
}
else {
cout << "False" ;
}
return 0;
}
|
Example 2
The below problem statement demonstrates one of the applications of the empty() function in C++ STL’s queue class.
Given a queue of integers, the task is to find the sum of all the integers.
Sample Input: 1, 8, 3, 6, 2
Sample Output: 20
Algorithm
- Check if the queue is empty, if not add the front element to a variable initialized as 0, and pop the front element.
- Repeat this step until the queue is empty.
- Print the final value of the variable.
Below is the implementation:
C++
#include <iostream>
#include <queue>
using namespace std;
int main()
{
int sum = 0;
queue< int > myqueue;
myqueue.push(1);
myqueue.push(8);
myqueue.push(3);
myqueue.push(6);
myqueue.push(2);
while (!myqueue.empty()) {
sum = sum + myqueue.front();
myqueue.pop();
}
cout << sum;
return 0;
}
|
queue::size()
size() function is used to return the size of the list container which is the number of elements currently stored in the list container.
Syntax
queuename.size()
Parameters
- This function does not accept any parameter.
Return Value
- It returns the number of elements stored in the container.
Examples
Input : myqueue = 1, 2, 3
myqueue.size();
Output : 3
Input : myqueue
myqueue.size();
Output : 0
Errors and Exceptions
- Shows an error if a parameter is passed.
- Shows no exception throw guarantee.
Examples of queue::size()
Example 1
The below C++ demonstrates the use of the size() function in C++ STL’s queue class.
C++
#include <iostream>
#include <queue>
using namespace std;
int main()
{
int sum = 0;
queue< int > myqueue;
myqueue.push(1);
myqueue.push(8);
myqueue.push(3);
myqueue.push(6);
myqueue.push(2);
cout << myqueue.size();
return 0;
}
|
Example 2
The below problem statement demonstrates one of the applications of the size() function in C++ STL’s queue class.
Given a queue of integers, find the sum of all the integers.
Sample Input : 1, 8, 3, 6, 2
Sample Output: 20
Algorithm
- Check if the size of the queue is zero, if not add the front element to a variable initialized as 0, and pop the front element.
- Repeat this step until the queue size becomes 0.
- Print the final value of the variable.
Below is the implementation:
C++
#include <iostream>
#include <queue>
using namespace std;
int main()
{
int sum = 0;
queue< int > myqueue;
myqueue.push(1);
myqueue.push(8);
myqueue.push(3);
myqueue.push(6);
myqueue.push(2);
while (myqueue.size() > 0) {
sum = sum + myqueue.front();
myqueue.pop();
}
cout << sum;
return 0;
}
|
Let us see the differences in a tabular form.
S.No. |
queue::empty() |
queue::size() |
1. |
It is used to return whether the queue is empty. |
It is used to return the number of elements in the queue. |
2. |
Its syntax is -: empty(); |
Its syntax is -: size(); |
3. |
It does not take any parameters. |
It does not take any parameters. |
4. |
Its return type is of boolean. |
Its return type is an integer. |
5. |
Its complexity is constant. |
Its complexity is constant. |
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