C++ Standard Template Library Practice Questions with Solutions

The Standard Template Library (STL) is one of the most powerful features of C++. It provides ready-made classes and functions that help developers write efficient, reusable, and high-performance programs without implementing common data structures and algorithms from scratch.

Instead of manually creating arrays, linked lists, stacks, or sorting algorithms, STL offers optimized implementations that are widely used in competitive programming, software development, and technical interviews. C++ Standard Template Library practice questions with solutions help to build concepts

The STL is divided into three major components:

• Containers
• Algorithms
• Iterators

What are Containers?

Containers are data structures that store collections of objects.

Common STL containers include:

• Vector
• List
• Queue
• Stack
• Deque
• Set
• Multiset
• Map
• Multimap
• Unordered Set
• Unordered Map

Example:

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int> numbers = {10, 20, 30};

    for (int number : numbers)
    {
        cout << number << " ";
    }

    return 0;
}

Output

10 20 30

What are Algorithms?

Algorithms perform operations on containers.

Common STL algorithms include:

• sort()
• reverse()
• find()
• count()
• binary_search()
• max_element()
• min_element()

Example:

sort(numbers.begin(), numbers.end());

What are Iterators?

Iterators are objects used to traverse container elements.

Example:

for(vector<int>::iterator it = numbers.begin(); it != numbers.end(); it++)
{
    cout << *it;
}

Advantages of STL

• Faster Development
• Optimized Performance
• Code Reusability
• Generic Programming
• Industry Standard
• Easy to Learn
• Useful for Competitive Programming

STL is widely used in

• Software Development
• Competitive Programming
• Data Processing
• Banking Software
• E-commerce Applications
• Machine Learning Projects
• System Programming

In this chapter, you’ll solve beginner-friendly STL practice questions.

Each question includes:

• Problem Statement
• Complete C++ Solution
• Sample Output
• Explanation
• Concepts Covered

Let’s begin.

1. C++ Program to Store Elements Using Vector

Problem Statement

Write a C++ program to store and display elements using a vector.

C++ Solution

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int> numbers = {10, 20, 30, 40, 50};

    for (int number : numbers)
    {
        cout << number << " ";
    }

    return 0;
}

Sample Output

10 20 30 40 50

Explanation

The vector stores multiple integers dynamically and allows easy traversal using a range-based loop.

Concepts Covered

• Vector
• Range-based Loop
• STL Container

2. C++ Program to Add Elements to a Vector

Problem Statement

Write a C++ program to insert elements into a vector using push_back().

C++ Solution

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int> numbers;

    numbers.push_back(5);
    numbers.push_back(10);
    numbers.push_back(15);

    for (int number : numbers)
    {
        cout << number << " ";
    }

    return 0;
}

Sample Output

5 10 15

Explanation

The push_back() function inserts elements at the end of the vector.

Concepts Covered

• Vector
• push_back()
• Dynamic Storage

3. C++ Program to Find the Size of a Vector

Problem Statement

Write a C++ program to display the number of elements stored in a vector.

C++ Solution

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int> numbers = {2,4,6,8,10};

    cout << "Size = "
         << numbers.size();

    return 0;
}

Sample Output

Size = 5

Explanation

The size() function returns the total number of elements stored in the vector.

Concepts Covered

• Vector
• size()
• STL Functions

4. C++ Program to Sort a Vector

Problem Statement

Write a C++ program to sort elements of a vector in ascending order.

C++ Solution

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
    vector<int> numbers = {25,10,30,5,20};

    sort(numbers.begin(), numbers.end());

    for(int number : numbers)
    {
        cout << number << " ";
    }

    return 0;
}

Sample Output

5 10 20 25 30

Explanation

The sort() algorithm arranges vector elements in ascending order.

Concepts Covered

• sort()
• Algorithm Library
• Vector

5. C++ Program to Reverse a Vector

Problem Statement

Write a C++ program to reverse the elements of a vector.

C++ Solution

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
    vector<int> numbers = {1,2,3,4,5};

    reverse(numbers.begin(), numbers.end());

    for(int number : numbers)
    {
        cout << number << " ";
    }

    return 0;
}

Sample Output

5 4 3 2 1

Explanation

The reverse() algorithm reverses the order of elements in the vector.

Concepts Covered

• reverse()
• Algorithm
• Vector

6. C++ Program to Demonstrate Stack Using STL

Problem Statement

Write a C++ program to demonstrate stack operations using the Standard Template Library.

C++ Solution

#include <iostream>
#include <stack>
using namespace std;

int main()
{
    stack<int> numbers;

    numbers.push(10);
    numbers.push(20);
    numbers.push(30);

    cout << "Top Element = "
         << numbers.top();

    return 0;
}

Sample Output

Top Element = 30

Explanation

A stack follows the LIFO (Last In, First Out) principle. The most recently inserted element is accessed first.

Concepts Covered

• Stack
• push()
• top()
• STL Container

7. C++ Program to Demonstrate Queue Using STL

Problem Statement

Write a C++ program to demonstrate queue operations using STL.

C++ Solution

#include <iostream>
#include <queue>
using namespace std;

int main()
{
    queue<int> numbers;

    numbers.push(10);
    numbers.push(20);
    numbers.push(30);

    cout << "Front Element = "
         << numbers.front() << endl;

    cout << "Back Element = "
         << numbers.back();

    return 0;
}

Sample Output

Front Element = 10
Back Element = 30

Explanation

A queue follows the FIFO (First In, First Out) principle. The first inserted element is removed first.

Concepts Covered

• Queue
• front()
• back()
• STL Queue

8. C++ Program to Demonstrate Set Using STL

Problem Statement

Write a C++ program to store unique elements using a set.

C++ Solution

#include <iostream>
#include <set>
using namespace std;

int main()
{
    set<int> numbers;

    numbers.insert(40);
    numbers.insert(10);
    numbers.insert(30);
    numbers.insert(20);
    numbers.insert(20);

    for(int number : numbers)
    {
        cout << number << " ";
    }

    return 0;
}

Sample Output

10 20 30 40

Explanation

A set automatically stores unique values in sorted order. Duplicate values are ignored.

Concepts Covered

• Set
• insert()
• Unique Elements

9. C++ Program to Demonstrate Map Using STL

Problem Statement

Write a C++ program to store key-value pairs using a map.

C++ Solution

#include <iostream>
#include <map>
using namespace std;

int main()
{
    map<int,string> students;

    students[101] = "Rahul";
    students[102] = "Priya";
    students[103] = "Amit";

    for(auto student : students)
    {
        cout << student.first
             << " "
             << student.second
             << endl;
    }

    return 0;
}

Sample Output

101 Rahul
102 Priya
103 Amit

Explanation

A map stores data as key-value pairs and automatically sorts the keys in ascending order.

Concepts Covered

• Map
• Key-Value Pair
• Associative Container

10. C++ Program to Traverse a Vector Using Iterators

Problem Statement

Write a C++ program to traverse a vector using iterators.

C++ Solution

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int> numbers = {5,10,15,20};

    vector<int>::iterator iterator;

    for(iterator = numbers.begin();
        iterator != numbers.end();
        iterator++)
    {
        cout << *iterator << " ";
    }

    return 0;
}

Sample Output

5 10 15 20

Explanation

Iterators provide a standard way to traverse elements stored inside STL containers.

Concepts Covered

• Iterator
• begin()
• end()
• Vector Traversal

11. C++ Program to Find an Element in a Vector Using find()

Problem Statement

Write a C++ program to search for an element in a vector using the STL find() algorithm.

C++ Solution

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
    vector<int> numbers = {10, 20, 30, 40, 50};

    auto iterator = find(numbers.begin(), numbers.end(), 30);

    if (iterator != numbers.end())
    {
        cout << "Element Found";
    }
    else
    {
        cout << "Element Not Found";
    }

    return 0;
}

Sample Output

Element Found

Explanation

The find() algorithm searches the container for the specified value. If found, it returns an iterator pointing to that element.

Concepts Covered

• find()
• Vector
• STL Algorithms

12. C++ Program to Find the Maximum Element in a Vector

Problem Statement

Write a C++ program to find the largest element in a vector.

C++ Solution

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
    vector<int> numbers = {45, 20, 90, 15, 65};

    cout << "Maximum Element = "
         << *max_element(numbers.begin(), numbers.end());

    return 0;
}

Sample Output

Maximum Element = 90

Explanation

The max_element() algorithm returns an iterator pointing to the largest element in the container.

Concepts Covered

• max_element()
• STL Algorithms
• Vector

13. C++ Program to Find the Minimum Element in a Vector

Problem Statement

Write a C++ program to find the smallest element in a vector.

C++ Solution

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
    vector<int> numbers = {45, 20, 90, 15, 65};

    cout << "Minimum Element = "
         << *min_element(numbers.begin(), numbers.end());

    return 0;
}

Sample Output

Minimum Element = 15

Explanation

The min_element() algorithm returns an iterator pointing to the smallest element in the vector.

Concepts Covered

• min_element()
• Vector
• STL Algorithms

14. C++ Program to Perform Binary Search Using STL

Problem Statement

Write a C++ program to perform binary search using the STL binary_search() function.

C++ Solution

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
    vector<int> numbers = {10, 20, 30, 40, 50};

    if (binary_search(numbers.begin(), numbers.end(), 30))
    {
        cout << "Element Found";
    }
    else
    {
        cout << "Element Not Found";
    }

    return 0;
}

Sample Output

Element Found

Explanation

The binary_search() function quickly checks whether an element exists in a sorted container.

Concepts Covered

• binary_search()
• STL Algorithms
• Searching

15. C++ Program to Count Occurrences of an Element Using STL

Problem Statement

Write a C++ program to count how many times a value appears in a vector.

C++ Solution

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
    vector<int> numbers = {10, 20, 30, 20, 40, 20};

    cout << "Occurrences of 20 = "
         << count(numbers.begin(), numbers.end(), 20);

    return 0;
}

Sample Output

Occurrences of 20 = 3

Explanation

The count() algorithm counts the number of occurrences of a specified value within the container.

Concepts Covered

• count()
• STL Algorithms
• Vector

Chapter Summary

In this chapter, you learned the fundamentals of the C++ Standard Template Library (STL). You explored commonly used containers such as vector, stack, queue, set, and map, along with iterators for container traversal. You also practiced powerful STL algorithms including sort(), reverse(), find(), max_element(), min_element(), binary_search(), and count(). Mastering STL helps you write cleaner, faster, and more efficient C++ programs while reducing development time.

Key Takeaways

• STL stands for Standard Template Library.
• STL consists of containers, algorithms, and iterators.
• vector is a dynamic array that automatically manages memory.
• stack follows the LIFO (Last In, First Out) principle.
• queue follows the FIFO (First In, First Out) principle.
• set stores unique values in sorted order.
• map stores data as key-value pairs with sorted keys.
• Iterators are used to traverse STL containers.
• STL algorithms simplify common tasks such as searching, sorting, reversing, and counting.
• STL is heavily used in competitive programming, coding interviews, and real-world software development.

Frequently Asked Questions (FAQs)

1. What is the Standard Template Library (STL) in C++?

The Standard Template Library (STL) is a collection of pre-built classes and algorithms that provide efficient implementations of common data structures and operations.

2. What are the three main components of STL?

The three main components are:

• Containers
• Algorithms
• Iterators

3. What is a vector in STL?

A vector is a dynamic array that automatically resizes itself as elements are added or removed.

4. What is the difference between a stack and a queue?

• Stack: Last In, First Out (LIFO)
• Queue: First In, First Out (FIFO)

5. Why is set useful?

A set automatically stores unique elements in sorted order, making it useful when duplicate values should not be allowed.

6. What is the purpose of iterators?

Iterators provide a standard way to access and traverse elements stored in STL containers.

7. Which header file contains STL algorithms like sort() and find()?

The <algorithm> header file contains most STL algorithms.

8. Why is STL important in C++?

STL improves productivity by providing optimized, reusable implementations of data structures and algorithms. It is widely used in competitive programming, technical interviews, and professional software development.

Written by Shubhranshu Shekhar, who has trained 20000+ students in coding.

Rishabh Kumar