C++ Stacks is a kind of container adaptor with a LIFO(Last In, First Out) type of working, where a new element is added at one end (top), and an element is removed from that end only. Stack uses an encapsulated object of either vector or deque (by default) or list (sequential container class) as its underlying container, providing a specific set of member functions to access its elements.
Header file required to use the stack in C++ – #include<stack>
With this, we can use stack STL.
Different functions associated with stacks
empty()
The empty() function returns whether the stack is empty or not.
Syntax
stack_name.empty()
We don’t pass any parameter, and it returns true if the stack is empty or false otherwise.
Example
stack1 = 1,2,3
stack1.empty();
Output
False size()
It returns several items in the stack.
Syntax
stack_name.size() We don’t pass any parameter in this; it returns the number of elements in the stack container.
Example
stack_1 = 1,2,3,4,5
stack_1.size();Output
5top()
It returns a reference to the topmost element of a stack.
Syntax
stack_name.top();
We don’t need to pass any parameter; it returns a direct reference of the top element.
Example
stack_name.push(5); stack_name.push(6); stack_name.top();
Output
6
push(k)
The push() function is used to insert the elements in the stack.
It adds the element ‘k’ at the top of the stack.
Syntax
stack_name.push(value)
In this, we pass the value as a parameter and, as a result, add the element to the stack.
Example
stack1.push(77) stack1.push(88)
Output
77, 88
pop()
It deletes the topmost element from the stack.
Syntax
stack_name.pop()
In this, we don’t pass any parameters. This function pops the topmost element from the stack.
Example
stack1 = 10,20,30; stack1.pop();
Output
10, 20
Errors and Exceptions
1. Shows error if a parameter is passed.
2. Shows no exception throw guarantee.
C++ Stack Algorithm
In stack-related algorithms, the TOP initially points to 0, the stack’s elements index starts from 1, and the index of the last element is MAX.
INIT_STACK (STACK, TOP)
Algorithm to initialize a stack using array.
TOP points to the top-most element of stack.
1) TOP: = 0;
2) Exit
The push() operation inserts an element into the stack.
PUSH_STACK(STACK,TOP,MAX,ITEM)
Algorithm to push an item into stack.
1) IF TOP = MAX then
Print “Stack is full”;
Exit;
2) Otherwise
TOP: = TOP + 1; /*increment TOP*/
STACK (TOP):= ITEM;
3) End of IF
4) Exit
The pop() operation is used to delete the item from the stack, get an item and then decrease the TOP pointer.
POP_STACK(STACK,TOP,ITEM)
Algorithm to pop an element from stack.
1) IF TOP = 0 then
Print “Stack is empty”;
Exit;
2) Otherwise
ITEM: =STACK (TOP);
TOP:=TOP – 1;
3) End of IF
4) Exit
IS_FULL(STACK,TOP,MAX,STATUS)
Algorithm to check stack is full or not.
STATUS contains the result status.
1) IF TOP = MAX then
STATUS:=true;
2) Otherwise
STATUS:=false;
3) End of IF
4) Exit
IS_EMPTY(STACK,TOP,MAX,STATUS)
Algorithm to check stack is empty or not.
STATUS contains the result status.
1) IF TOP = 0 then
STATUS:=true;
2) Otherwise
STATUS:=false;
3) End of IF
4) Exit
C++ Stack Program
Q1- Write a program to insert five elements in the stack and print the top element using top(), print the stack size, and check if the stack is empty.
#include <iostream>
#include <stack>
using namespace std;
int main()
{
stack<int> stack1; //empty stack of integer type
stack1.push(100);
stack1.push(200);
stack1.push(300);
stack1.push(400);
stack1.push(500);
cout << "The topmost element of the stack is:" << stack1.top() << endl;
cout << "The size of the stack is=" << stack1.size() << endl;
if (stack1.empty())
{
cout << "Stack is empty" << endl;
}
else
{
cout << "Stack is not empty" << endl;
}
}
See the output.
Q2- Write a program to insert 5 elements in a stack, delete 2 elements, and print the stack.
#include <iostream>
#include <stack>
using namespace std;
int main()
{
stack<int> stack1; //empty stack of integer type
stack1.push(100);
stack1.push(200);
stack1.push(300);
stack1.push(400);
stack1.push(500);
stack1.pop();
stack1.pop();
while (!stack1.empty())
{
cout << "Element =" << stack1.top() << endl;
stack1.pop();
}
}
See the output.
That’s it.
Ankit Lathiya is a Master of Computer Application by education and Android and Laravel Developer by profession and one of the authors of this blog. He is also expert in JavaScript and Python development.
