chapter 04 exercise solution

udemy-cpp/exc04/IteratorLib.h

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+#include <cstdint>
+#include <iterator>
+#include <vector>
+
+namespace mystd
+{
+
+using It = std::vector<std::int32_t>::iterator;
+using DifferenceType = It::difference_type;
+
+/* advence: advances iterator it by n steps */
+void advance(It &it, DifferenceType n)
+{
+    it += n;
+}
+
+/* distance: returns number of steps needed to go from first to last */
+DifferenceType distance(It first, It last)
+{
+    auto dist = DifferenceType{0};
+
+    for (; first < last; ++dist)
+        ++first;
+    for (; first > last; --dist)
+        --first;
+
+    return dist;
+}
+
+/* next: returns next iterator */
+It next(It it, DifferenceType n = 1)
+{
+    return it + n;
+}
+
+/* prev: returns previous iterator */
+It prev(It it, DifferenceType n = 1)
+{
+    return it - n;
+}
+
+} // namespace mystd

udemy-cpp/exc04/main.cc

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+#include <iostream>
+#include <vector>
+
+#include "IteratorLib.h"
+
+int main()
+{
+    auto vector = std::vector<int>{1, 2, 3};
+    auto vector_it = vector.begin();
+
+    auto next_it = mystd::next(vector_it);
+    std::cout << "*next_it: " << *next_it << '\n';
+
+    auto prev_it = mystd::prev(next_it);
+    std::cout << "*prev_it: " << *prev_it << '\n';
+
+    mystd::advance(vector_it, 2);
+    std::cout << "advance: " << *vector_it << '\n';
+
+    auto dist = mystd::distance(vector_it, vector.begin());
+    std::cout << "distance: " << dist << '\n';
+
+    return 0;
+}