CppHow-ToBeginner · 3 min read

How to Use Stack in C++: Syntax and Examples

In C++, you use the stack container from the <stack> header to store elements in a last-in, first-out (LIFO) order. You can add elements with push(), remove with pop(), and access the top element with top().

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Syntax

The stack is a container adapter that works on top of other containers like vector or deque. Here is the basic syntax:

std::stack<Type> stackName; - declares a stack of elements of type Type.
push(value) - adds value to the top of the stack.
pop() - removes the top element.
top() - returns the top element without removing it.
empty() - checks if the stack is empty.
size() - returns the number of elements.

cpp

std::stack<Type> stackName;
stackName.push(value);
stackName.pop();
Type topValue = stackName.top();
bool isEmpty = stackName.empty();
size_t count = stackName.size();

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Example

This example shows how to create a stack of integers, add elements, access the top, and remove elements until the stack is empty.

cpp

#include <iostream>
#include <stack>

int main() {
    std::stack<int> numbers;

    // Add elements
    numbers.push(10);
    numbers.push(20);
    numbers.push(30);

    // Access and remove elements
    while (!numbers.empty()) {
        std::cout << "Top element: " << numbers.top() << std::endl;
        numbers.pop();
    }

    return 0;
}

Output

Top element: 30 Top element: 20 Top element: 10

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Common Pitfalls

Common mistakes when using stack include:

Calling top() or pop() on an empty stack causes undefined behavior (usually a crash).
Forgetting that pop() does not return the removed element; you must call top() before pop() to access it.
Assuming stack supports iteration — it does not because it is a container adapter.

cpp

/* Wrong way: calling top() on empty stack */
#include <stack>
#include <iostream>

int main() {
    std::stack<int> s;
    // std::cout << s.top(); // ERROR: stack is empty
    if (!s.empty()) {
        std::cout << s.top(); // Safe way
    }
    return 0;
}

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Quick Reference

Remember these key functions for std::stack:

Function	Description
push(value)	Add element to the top
pop()	Remove top element
top()	Access top element
empty()	Check if stack is empty
size()	Get number of elements

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Key Takeaways

Use push() to add and pop() to remove elements from the stack.

Always check empty() before calling top() or pop() to avoid errors.

stack follows last-in, first-out (LIFO) order.

pop() does not return the removed element; use top() first to access it.

stack does not support iteration like other containers.