Iterators

Questions 1 to 5 of 7

1. 1. What is the bug in this loop? ``cpp #include <iostream> #include <vector> int main() { std::vector<int> v{4, -1, 7, -3, 9}; for (auto it = v.begin(); it != v.end(); ++it) { if (*it < 0) { v.erase(it); } } for (int x : v) std::cout << x << ' '; } ``

   The loop should stop at begin() instead of end()erase makes it invalid, and the ++it in the loop header then moves that invalid iterator, so the result is undefined. Store the return value of erase in it, and move forward only when nothing was erasedv must be declared const before the loopThe test *it < 0 should be *it <= 0
2. 2. What is wrong with this code? ``cpp #include <iostream> #include <vector> int main() { std::vector<int> v{5, 6}; auto first = v.begin(); v.push_back(7); std::cout << *first << '\n'; } ``

   first cannot point into the vector, because the vector has only two itemspush_back sorts the items, so first points at the wrong valueThe vector is full at capacity 2, so push_back moves the items to a new block and frees the old one, which leaves first pointing at freed memorystd::cout cannot print an int that came from an iterator
3. 3. What happens when this program runs? ``java import java.util.ArrayList; import java.util.List; public class Main { public static void main(String[] args) { List<String> names = new ArrayList<>(List.of("Ana", "Ben", "Cara")); for (String name : names) { if (name.equals("Ana")) { names.remove(name); } } System.out.println(names); } } ``

   It prints [Ben, Cara], because the loop does not notice the removalIt prints [Ana, Ben, Cara], because remove does nothing inside a for-each loopIt prints [Ben], because the loop skips the second itemIt throws ConcurrentModificationException, because the list changed while the for-each loop was still using its iterator
4. 4. What does this program print? ``cpp #include <iostream> #include <vector> int main() { std::vector<int> v{4, 5, 6, 7, 8}; for (auto it = v.begin(); it != v.end();) { if (*it % 2 == 0) { it = v.erase(it); } else { ++it; } } for (int x : v) std::cout << x << ' '; } ``

   5 74 6 85 7 85 6 7
5. 5. What does this program print? ``java import java.util.ArrayList; import java.util.List; public class Main { public static void main(String[] args) { List<String> names = new ArrayList<>(List.of("Ana", "Ben", "Cara", "Dev")); names.removeIf(n -> n.startsWith("C")); System.out.println(names); } } ``

   [Ana, Ben, Cara, Dev][Ben, Dev][Ana, Ben, Dev][Ana, Dev]