क्लास टेम्पलेट और CTAD

#include <vector>
#include <stdexcept>
#include <iostream>

template <typename T>
class Stack {
private:
    std::vector<T> elements_;

public:
    void push(const T& value);
    void pop();
    const T& top() const;
    bool empty() const { return elements_.empty(); }
    std::size_t size() const { return elements_.size(); }
};

// Member definitions outside the class require the template header
template <typename T>
void Stack<T>::push(const T& value) {
    elements_.push_back(value);
}

template <typename T>
void Stack<T>::pop() {
    if (elements_.empty()) {
        throw std::out_of_range("Stack<>::pop(): empty stack");
    }
    elements_.pop_back();
}

template <typename T>
const T& Stack<T>::top() const {
    if (elements_.empty()) {
        throw std::out_of_range("Stack<>::top(): empty stack");
    }
    return elements_.back();
}

int main() {
    Stack<int> intStack;
    intStack.push(42);
    intStack.push(17);
    std::cout << intStack.top() << '\n'; // 17
    intStack.pop();
    std::cout << intStack.top() << '\n'; // 42
}

#include <vector>
#include <deque>
#include <iostream>

// Container defaults to std::deque<T> — matches std::stack's design
template <typename T, typename Container = std::deque<T>>
class Stack {
private:
    Container elements_;

public:
    void push(const T& value) { elements_.push_back(value); }
    void pop()                { elements_.pop_back(); }
    const T& top() const      { return elements_.back(); }
    bool empty() const        { return elements_.empty(); }
};

int main() {
    Stack<int> s1;                         // uses deque<int>
    Stack<int, std::vector<int>> s2;       // uses vector<int>

    s1.push(10);
    s2.push(20);
    std::cout << s1.top() << '\n'; // 10
    std::cout << s2.top() << '\n'; // 20
}

#include <iostream>
#include <cstddef>

template <typename T, std::size_t N>
struct Array {
    T data[N];
};

// Without a deduction guide, CTAD cannot deduce T and N.
// This explicit deduction guide maps brace-init with N elements
// of the same type T to Array<T, N>.
template <typename First, typename... Rest>
Array(First, Rest...) -> Array<First, 1 + sizeof...(Rest)>;

// Standard library example: std::vector CTAD from iterators
#include <vector>
#include <list>

int main() {
    // CTAD with our custom deduction guide
    Array arr{1, 2, 3, 4, 5};  // deduces Array<int, 5>
    std::cout << arr.data[2] << '\n'; // 3

    // Standard library CTAD examples (C++17)
    std::pair p(42, 3.14);       // pair<int, double>
    std::vector v{1, 2, 3};     // vector<int>
    std::tuple t(1, 2.0, 'a');  // tuple<int, double, char>

    // CTAD from iterator range
    std::list<int> lst{10, 20, 30};
    std::vector v2(lst.begin(), lst.end()); // vector<int>
}