cpp-flashcards/org/cpp/iterator.org

• What is a C++ iterator
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• Task: Traverse a vector with iterators
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• Iterator operations
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• cpp iterator categories
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• Task: Use const iterator
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• Task: Use reverse iterator
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• Minimal custom iterator implementation
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• When to use iterators vs indices
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What is a C++ iterator   cpp iterator concept recognition

Front

What is an iterator in C++?

Back

An object that points to elements in a container and allows traversal through them, providing a common interface for accessing elements sequentially without exposing the underlying structure.

Task: Traverse a vector with iterators   cpp iterator production code

Front

Write C++ code to iterate through a std::vector<int> using iterators

Back

std::vector<int> vec = {1, 2, 3};
for (auto it = vec.begin(); it != vec.end(); ++it) {
    std::cout << *it << " ";
}

Iterator operations   cpp iterator concept enumeration

Front

What are the four required operations for a C++ iterator?

Back

• `operator*` — dereference to get current element
• `operator++` — advance to next element (pre and post)
• `operator==` — equality comparison
• `operator!=` — inequality comparison

cpp iterator categories   cpp iterator concept enumeration

Front

List the five iterator categories in C++ (from simplest to most advanced)

Back

1. Input Iterator — read values, advance once
2. Output Iterator — write values, advance once
3. Forward Iterator — read/write, multiple passes
4. Bidirectional Iterator — + operator–
5. Random Access Iterator — + arithmetic, subscript

Task: Use const iterator   cpp iterator production code

Front

Write C++ code to safely traverse a const std::vector without modifying elements

Back

std::vector<int> vec = {1, 2, 3};
for (auto it = vec.cbegin(); it != vec.cend(); ++it) {
    std::cout << *it << " ";
}

Task: Use reverse iterator   cpp iterator production code

Front

Write C++ code to iterate backwards through a std::vector

Back

std::vector<int> vec = {1, 2, 3};
for (auto it = vec.rbegin(); it != vec.rend(); ++it) {
    std::cout << *it << " ";
}

Minimal custom iterator implementation   cpp iterator implementation production

Front

Write the minimal C++ code to implement a forward iterator for a custom class

Back

class MyIterator {
    Node* ptr;
public:
    reference operator*() const { return ptr->data; }
    pointer operator->() const { return &ptr->data; }
    MyIterator& operator++() { ptr = ptr->next; return *this; }
    MyIterator operator++(int) { auto tmp = *this; ++*this; return tmp; }
    bool operator==(const MyIterator& other) const { return ptr == other.ptr; }
    bool operator!=(const MyIterator& other) const { return !(*this == other); }
};

When to use iterators vs indices   cpp iterator concept comparison

Front

When would you choose iterators over index-based loops in C++?

Back

• Container type is unknown or could change (iterators abstract the container)
• Using standard library algorithms (std::find, std::sort, etc.)
• Need to traverse multiple containers simultaneously
• Working with containers without random access (list, map)
• Decouple algorithm from container structure