Implementing IntList, Phase 2: The Iteratorizing

In principle, you now know how the iterator is supposed to work, so now it's time to implement it. Once again, we'll break this work into two parts: planning and implementation.

Your Task, Part 1: Planning the Implementation

You will need to do the following:

• Think about how how all the pieces work, and how they fit together, including
  • What begin() and end() need to do.
  • What the ++, *, and != operators of the iterator need to do.
• Capture evidence of your planning as a .jpg file (either a photo of your nodes, whiteboard session, or a screenshot of your digital drawing), adding it to the Planning folder in your repository as Phase_2.jpg.

Your Task, Part 2: Implementing and Testing

Implementing the Missing Functions

In intlist.cpp, add the following code:

IntList::const_iterator IntList::begin() const {
    // TODO: use the iterator constructor to create an iterator refering
    //       to the first node
}

IntList::const_iterator IntList::end() const {
    // TODO: use the iterator constructor to create an iterator with the
    //       correct value to represent "just gone off the end"
}


IntList::Iter::Iter(Node* current) /* TODO: member initializer list */ {
    // TODO: any other code you need or perhaps nothing else needed
}

IntList::Iter& IntList::Iter::operator++() {
    // TODO: advance the iterator to the next node

    // return ourselves to allow chained increments
    return *this;
}

const int& IntList::Iter::operator*() const {
    // TODO: return the value in the current node
}

bool IntList::Iter::operator==(const Iter& rhs) const {
    // TODO: compare this iterator with another for equality
}

bool IntList::Iter::operator!=(const Iter& rhs) const {
    return !(*this == rhs); // use the == operator we just wrote
}

None of these functions change the structure of the list, so you don't need to call check_invariants() in any of them, but you can do so in begin() and end() if you want to.

Testing the Iterator

Now you can try your newly written iterator with your newly written test cases in intlist-test.cpp.

cs70-make -H intlist-test
./intlist-test

If all the tests pass, great! But if not, running with valgrind will give you a backtrace that will help you find the problem:

valgrind --leak-check=full ./intlist-test

All the usual debugging advice applies here. If you get stuck, you can post on Piazza, or ask in grutoring hours or during lab.

Your Task, Part 3: Revising the Snake Game to Use the Iterator

Now that we have a working IntList class, let's switch the Snake game to use it instead of IntVector. Open config.hpp and replace the code in the marked section with this new code:

#define COORDLIST_USES_INTLIST 1
#define COORDLIST_PROVIDES_ITERATOR 1

Then run

cs70-make -H snake
./snake

Hopefully the game will still work (and show the desired effect when the game ends). If it doesn't work, it may indicate that you have a bug in your IntList class not captured by your test cases. You may be able to get some insight by running the game under valgrind, but do not spend significant time trying to understand the internal logic of the Snake game. If you can't find anything obvious wrong with your IntList class, ask for help on Piazza, during grutoring hours, or during lab, but you can move on to the next part of the assignment without getting this part working.

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