#define CATCH_CONFIG_MAIN
#include <catch2/catch.hpp>

int _testmain();

#include <vector>

int count_in_range(std::vector<int>::iterator first, std::vector<int>::iterator last);

TEST_CASE("count_in_range returns full vector size", "[count_in_range]") {
    std::vector<int> v{10, 20, 30, 40, 50};
    REQUIRE(count_in_range(v.begin(), v.end()) == 5);
}

TEST_CASE("count_in_range returns partial range size", "[count_in_range]") {
    std::vector<int> v{10, 20, 30, 40, 50};
    REQUIRE(count_in_range(v.begin(), v.begin() + 3) == 3);
}

TEST_CASE("count_in_range returns 0 for empty range", "[count_in_range]") {
    std::vector<int> v{10, 20, 30, 40, 50};
    REQUIRE(count_in_range(v.begin() + 2, v.begin() + 2) == 0);
}

TEST_CASE("count_in_range works on single element range", "[count_in_range]") {
    std::vector<int> v{10, 20, 30, 40, 50};
    REQUIRE(count_in_range(v.begin() + 4, v.end()) == 1);
}

TEST_CASE("count_in_range works on empty vector", "[count_in_range]") {
    std::vector<int> v;
    REQUIRE(count_in_range(v.begin(), v.end()) == 0);
}

test.cpp

This course explains how iterators work in the C++ Standard Template Library and how they connect containers and algorithms. You will learn what iterators are, how different iterator categories behave, and how to use them safely and idiomatically with STL containers and algorithms. By the end of the course, you will confidently read, write, and reason about iterator-based code, including const iterators, reverse iterators, and iterator invalidation rules.

Learn the foundational concepts of iterators, their purpose in the STL, and how to use them for basic container traversal.

Delve into the different categories of iterators, their capabilities, and which containers support each category.

Investigate how iterators behave with different STL containers, including sequence and associative containers, and the importance of const iterators.

Learn how STL algorithms interact with iterators, how to use them safely, and how to avoid iterator invalidation.

Challenge: Count Elements in an Iterator Range

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