stack empty() and stack size() in C++ STL

Stacks are a type of container adaptors with LIFO(Last In First Out) type of working, where a new element is added at one end and (top) an element is removed from that end only.

stack::empty()

empty() function is used to check if the stack container is empty or not.

Syntax :

stackname.empty()
Parameters :
No parameters are passed.
Returns :
True, if stack is empty
False, Otherwise

Examples:

Input :   mystack
          mystack.empty();
Output :  True
 
Input :   mystack = 1, 2, 3
Output :  False

Errors and Exceptions



1. Shows error if parameter is passed
2. Shows no exception throw guarantee.

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// CPP program to illustrate
// Implementation of empty() function
#include <iostream>
#include <stack>
using namespace std;
  
int main()
{
    stack<int> mystack;
    mystack.push(1);
  
    // Stack becomes 1
  
    if (mystack.empty()) {
        cout << "True";
    }
    else {
        cout << "False";
    }
    return 0;
}

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Output:


False



Application :

Given a stack of integers, find the sum of the all the integers.


Input : 1, 8, 3, 6, 2
Output: 20



Algorithm

1. Check if the stack is empty, if not add the top element to a variable initialised as 0, and pop the top element.

2. Repeat this step until the stack is empty.

3. Print the final value of the variable.











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// CPP program to illustrate 


// Application of empty() function 


#include <iostream> 


#include <stack> 


using namespace std; 


  


int main() 


{ 


    int sum = 0; 


    stack<int> mystack; 


    mystack.push(1); 


    mystack.push(8); 


    mystack.push(3); 


    mystack.push(6); 


    mystack.push(2); 


  


    // Stack becomes 1, 8, 3, 6, 2 


  


    while (!mystack.empty()) { 


        sum = sum + mystack.top(); 


        mystack.pop(); 


    } 


    cout << sum; 


    return 0; 


} 



















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Output:


20



stack::size()


size() function is used to return the size of the stack container or the number of elements in the stack container.


Syntax :


stackname.size()
Parameters :
No parameters are passed.
Returns :
Number of elements in the container.



Examples:




Input :   mystack = 0, 1, 2
          mystack.size();
Output :  3
 
Input :   mystack = 0, 1, 2, 3, 4, 5
          mystack.size();
Output :  6



Errors and Exceptions


1. Shows error if a parameter is passed.

2. Shows no exception throw guarantee.











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// CPP program to illustrate 


// Implementation of size() function 


#include <iostream> 


#include <stack> 


using namespace std; 


  


int main() 


{ 


    int sum = 0; 


    stack<int> mystack; 


    mystack.push(1); 


    mystack.push(8); 


    mystack.push(3); 


    mystack.push(6); 


    mystack.push(2); 


  


    // Stack becomes 1, 8, 3, 6, 2 


  


    cout << mystack.size(); 


  


    return 0; 


} 



















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Output:


5



Application :

Given a stack of integers, find the sum of the all the integers.


Input : 1, 8, 3, 6, 2
Output: 20



Algorithm

1. Check if the size of the stack is zero, if not add the top element to a variable initialised as 0, and pop the top element.

2. Repeat this step until the stack size becomes 0.

3. Print the final value of the variable.











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                                    close




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                                    brightness_4

                                    code
                                




















// CPP program to illustrate 


// Application of size() function 


#include <iostream> 


#include <stack> 


using namespace std; 


  


int main() 


{ 


    int sum = 0; 


    stack<int> mystack; 


    mystack.push(1); 


    mystack.push(8); 


    mystack.push(3); 


    mystack.push(6); 


    mystack.push(2); 


  


    // Stack becomes 1, 8, 3, 6, 2 


  


    while (mystack.size() > 0) { 


        sum = sum + mystack.top(); 


        mystack.pop(); 


    } 


    cout << sum; 


    return 0; 


} 



















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Output:


20





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