इटरेटर: STL को जोड़ने वाली कड़ी

#include <vector>
#include <list>
#include <algorithm>
#include <iostream>
#include <iterator>

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

    // Member functions
    auto first = vec.begin();   // points to 5
    auto last  = vec.end();     // points past 2

    // Free functions — preferred for generic code
    auto first2 = std::begin(vec);
    auto last2  = std::end(vec);

    // Works with C-arrays too
    int arr[] = {10, 20, 30};
    std::sort(std::begin(arr), std::end(arr));

    // const iterators — read-only access
    auto cit = vec.cbegin();     // const_iterator
    // *cit = 99;                // ERROR: cannot modify through const_iterator

    // Reverse iterators — iterate backward
    for (auto rit = vec.rbegin(); rit != vec.rend(); ++rit) {
        std::cout << *rit << ' ';  // 2, 4, 1, 3, 5 (reversed, pre-sort was applied)
    }
    std::cout << '\n';
}

#include <iterator>
#include <vector>
#include <list>
#include <iostream>

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

    // std::next — returns iterator n positions forward (default 1)
    auto it = std::next(vec.begin(), 2);   // points to 30
    std::cout << *it << '\n';              // 30

    // std::prev — returns iterator n positions backward
    auto it2 = std::prev(vec.end());       // points to 50
    std::cout << *it2 << '\n';             // 50

    // std::advance — modifies iterator in place (no return)
    auto it3 = vec.begin();
    std::advance(it3, 3);                  // now points to 40
    std::cout << *it3 << '\n';             // 40

    // std::distance — number of increments from first to last
    auto d = std::distance(vec.begin(), vec.end());  // 5
    std::cout << "Distance: " << d << '\n';

    // These work with non-random-access iterators too
    std::list<int> lst = {1, 2, 3, 4, 5};
    auto lit = std::next(lst.begin(), 2);  // O(n) for list, O(1) for vector
    std::cout << *lit << '\n';             // 3

    auto ld = std::distance(lst.begin(), lst.end());  // O(n) for list
    std::cout << "List distance: " << ld << '\n';     // 5
}

#include <iterator>
#include <vector>
#include <algorithm>
#include <iostream>
#include <sstream>

int main() {
    std::vector<int> src = {1, 2, 3, 4, 5};
    std::vector<int> dst;

    // back_inserter — calls push_back on each assignment
    std::copy(src.begin(), src.end(), std::back_inserter(dst));
    // dst: {1, 2, 3, 4, 5}

    // front_inserter — calls push_front (works with deque, list)
    // inserter — calls insert at a given position

    // ostream_iterator — write to an output stream
    std::copy(dst.begin(), dst.end(),
              std::ostream_iterator<int>(std::cout, ", "));
    std::cout << '\n';  // 1, 2, 3, 4, 5,

    // istream_iterator — read from an input stream
    std::istringstream iss("10 20 30 40");
    std::vector<int> from_stream(
        std::istream_iterator<int>(iss),
        std::istream_iterator<int>()   // end-of-stream sentinel
    );
    // from_stream: {10, 20, 30, 40}
}