Advanced C++ Practice

Practise lambdas, templates, exceptions, file streams, std::optional and move semantics in modern C++.

Advanced7 problemsUpdated October 23, 2026

Review first: Lambdas, Templates, Exceptions, File Handling, Move Semantics and the Rule of Five, Modern C++ Features

1.Lambdas with captures

Advanced

Given std::vector<int> nums = {4, 11, 7, 20, 15, 2}; and int limit = 10;, use std::count_if with a lambda that captures limit to count the numbers above it. Then use std::for_each with a lambda that captures a total by reference to add up all the numbers.

Show hint

Capture by value with [limit] and by reference with [&total].

Show solution

C++

#include <algorithm>
#include <iostream>
#include <vector>

int main() {
    std::vector<int> nums = {4, 11, 7, 20, 15, 2};
    int limit = 10;

    auto above = std::count_if(nums.begin(), nums.end(), [limit](int n) { return n > limit; });

    int total = 0;
    std::for_each(nums.begin(), nums.end(), [&total](int n) { total += n; });

    std::cout << above << ' ' << total << '\n';
}

Output

3 59

2.A function template

Advanced

Write a function template T largest(const std::vector<T>& v) that returns the largest element, and use it with {3, 9, 4}, {2.5, 1.5} and a vector of strings {"pear", "apple", "plum"}.

Show hint

template <typename T> before the function. Start from v[0] and compare with >.

Show solution

C++

#include <iostream>
#include <string>
#include <vector>

template <typename T>
T largest(const std::vector<T>& v) {
    T best = v[0];
    for (const T& x : v) {
        if (x > best) best = x;
    }
    return best;
}

int main() {
    std::cout << largest(std::vector<int>{3, 9, 4}) << ' '
              << largest(std::vector<double>{2.5, 1.5}) << ' '
              << largest(std::vector<std::string>{"pear", "apple", "plum"}) << '\n';
}

Output

9 2.5 plum

Strings compare alphabetically, so "plum" is the largest of the three.

3.A class template

Advanced

Write template <typename K, typename V> struct Entry { K key; V value; }; and a function template print(const Entry<K, V>&) that prints key = value. Use it with Entry<std::string, int>{"age", 21} and Entry<char, double>{'x', 2.5}.

Show hint

The print function needs the same two template parameters: template <typename K, typename V>.

Show solution

C++

#include <iostream>
#include <string>

template <typename K, typename V>
struct Entry {
    K key;
    V value;
};

template <typename K, typename V>
void print(const Entry<K, V>& e) {
    std::cout << e.key << " = " << e.value << '\n';
}

int main() {
    print(Entry<std::string, int>{"age", 21});
    print(Entry<char, double>{'x', 2.5});
}

Output

age = 21
x = 2.5

4.Handle bad input with exceptions

Advanced

For each of "42", "abc" and "99999999999", convert the text with std::stoi and print the number, or invalid for std::invalid_argument, or too large for std::out_of_range.

Show hint

std::stoi throws std::invalid_argument when there is no number, and std::out_of_range when the value does not fit in an int.

Show solution

C++

#include <iostream>
#include <stdexcept>
#include <string>

int main() {
    for (std::string text : {"42", "abc", "99999999999"}) {
        try {
            int value = std::stoi(text);
            std::cout << text << ": " << value << '\n';
        } catch (const std::invalid_argument&) {
            std::cout << text << ": invalid\n";
        } catch (const std::out_of_range&) {
            std::cout << text << ": too large\n";
        }
    }
}

Output

42: 42
abc: invalid
99999999999: too large

5.Write and read a file

Advanced

Write three lines Asha 92, Ravi 85 and Meera 78 to scores.txt. Then read the file back with >> and print the name of the top scorer and the average score.

Show hint

Use std::ofstream to write and std::ifstream to read; while (in >> name >> score) reads pairs until the end.

Show solution

C++

#include <fstream>
#include <iostream>
#include <string>

int main() {
    {
        std::ofstream out("scores.txt");
        out << "Asha 92\nRavi 85\nMeera 78\n";
    }

    std::ifstream in("scores.txt");
    std::string name;
    int score = 0;
    std::string best_name;
    int best = -1;
    int total = 0;
    int count = 0;

    while (in >> name >> score) {
        total += score;
        ++count;
        if (score > best) {
            best = score;
            best_name = name;
        }
    }
    std::cout << best_name << ' ' << static_cast<double>(total) / count << '\n';
}

Output

Asha 85

6.Return an optional

Advanced

Write std::optional<int> find_age(const std::map<std::string, int>& ages, const std::string& name) that returns the age or std::nullopt. Print the result for "Asha" and, using value_or(-1), for "John".

Show hint

Use ages.find(name) and compare with ages.end().

Show solution

C++

#include <iostream>
#include <map>
#include <optional>
#include <string>

std::optional<int> find_age(const std::map<std::string, int>& ages, const std::string& name) {
    if (auto it = ages.find(name); it != ages.end()) {
        return it->second;
    }
    return std::nullopt;
}

int main() {
    std::map<std::string, int> ages = {{"Asha", 21}, {"Ravi", 25}};

    if (auto age = find_age(ages, "Asha")) {
        std::cout << "Asha is " << *age << '\n';
    }
    std::cout << find_age(ages, "John").value_or(-1) << '\n';
}

Output

Asha is 21
-1

7.Move instead of copy

Advanced

Create a std::vector<std::unique_ptr<std::string>> and add three heap-allocated strings to it. One of them is first created in a local unique_ptr and then moved in. Print the strings, and whether the local pointer is empty afterwards.

Show hint

A unique_ptr cannot be copied into the vector; use push_back(std::move(local)).

Show solution

C++

#include <iostream>
#include <memory>
#include <string>
#include <utility>
#include <vector>

int main() {
    std::vector<std::unique_ptr<std::string>> items;
    items.push_back(std::make_unique<std::string>("first"));

    auto local = std::make_unique<std::string>("second");
    items.push_back(std::move(local));

    items.push_back(std::make_unique<std::string>("third"));

    for (const auto& item : items) std::cout << *item << ' ';
    std::cout << '\n' << std::boolalpha << (local == nullptr) << '\n';
}

Output

first second third
true

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