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

19 Sep, 2018
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.
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 passed2. Shows no exception throw guarantee.
// 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;}
Output:
False

Application :Given a stack of integers, find the sum of the all the integers.
Input : 1, 8, 3, 6, 2
Output: 20

Algorithm1. 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.
// 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;}
Output:
20

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.
// 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;}
Output:
5

Application :Given a stack of integers, find the sum of the all the integers.
Input : 1, 8, 3, 6, 2
Output: 20

Algorithm1. 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.
// 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;}
Output:
20

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CPP-Library
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