Question

1\. Suppose that you have the following C++ code: vector myList(5); unsigned int length; myList[0] = 3; for (int i = 1; i < 4; i++) myList[i] = 2 * myList[i - 1] - 5; myList.push_back(46); myList.push_back(57); myList.push_back(35); a. Write a C++ statement that outputs the first and the last elements of myList. (Do not use the array subscripting operator or the index of the elements.) b. Write a C++ statement that stores the size of myList into length. c. Write a for loop that outputs the elements of myList.

Short answer

Use `myList.front()` and `myList.back()` to access first and last elements. Use `myList.size()` for length. Output elements with a range-based for loop.

Step-by-step solution

Initialize vector and populate

The code initializes a vector `myList` with 5 integers, setting the initial elements to zero. Then `myList[0]` is set to 3. A loop populates `myList[1]` to `myList[3]` using the formula `2 * myList[i - 1] - 5`. Then elements 46, 57, and 35 are pushed to the end of the vector.

Determine first and last elements without subscripting

To output the first and last elements of the vector `myList` without using subscripting, we utilize iterators. In C++, you can do this by using `myList.front()` to access the first element and `myList.back()` to access the last element.

Store size of vector into length

To store the size of `myList` into `length`, the method `myList.size()` is used. This gives the total number of elements in the vector and can be stored directly into `length`.

Write a for loop to output elements

To output each element in `myList`, a for loop iterating over the vector using an iterator is used. In C++, this can be accomplished either with a range-based for loop or an iterator from begin to end. The range-based loop looks like: `for(auto elem : myList) { cout << elem << " "; }`.

Key concepts

Vectors in C++

Vectors in C++ are a type of sequence container representing arrays that can grow dynamically. They are part of the Standard Template Library (STL) and provide several advantages over traditional arrays:

• **Dynamic Sizing:** Unlike arrays, vectors can change in size, making them flexible and convenient when working with data collections that vary. You do not have to specify the size upfront.
• **Access Elements:** You can access elements using the `at()` method or directly through subscripting (e.g., `vec[i]`). However, STL provides additional methods such as `front()` and `back()`.
• **Memory Management:** Vectors manage the storage automatically, growing as necessary by allocating new memory and deallocating old memory as needed.

Understanding how vectors work is crucial for effective C++ programming because they combine the clarity of arrays with the dynamic properties of linked lists, giving you the best of both worlds.

Iterators in C++

Iterators in C++ are objects that facilitate the traversal and manipulation of elements in containers like vectors. They perform a role akin to pointers in arrays, allowing programmers to navigate through the data.

• **Types of Iterators:** Iterators can be constant, mutable, or reverse. The type used depends on the needed operations and whether modification of elements is required.
• **Using Iterators:** Use `begin()` and `end()` to get iterators pointing to the start and just past the last element of the container. For instance, iterating through a vector can be achieved with a `for` loop using these iterators.
• **Advantages:** Iterators help in abstracting container details, ensuring code compatibility across different container types by using the same iterator interface.

Iterators are essential in C++ as they provide a standard way of operating on containers, leading to more readable and efficient code.

Range-Based For Loop

The range-based for loop in C++ is a simplified looping construct for iterating over elements in a container like vectors. Introduced in C++11, it enhances readability and reduces the likelihood of errors in your code.

• **Syntax:** The syntax is `for (auto &element : container)`, where `element` takes on each successive value from the container.
• **Benefits:** It requires fewer lines of code compared to traditional loops and minimizes the risks associated with incorrect indexing.
• **Use Cases:** Best for situations where you need to access elements without modifying them, ensuring easy iteration through all elements of a container.

The range-based for loop simplifies iteration and makes code cleaner and easier to understand.

C++ STL Methods

C++ Standard Template Library (STL) provides a range of methods that make handling data structures like vectors more intuitive and less error-prone.

• **Common Methods:** Methods such as `push_back()` add elements to the end of a vector, `size()` returns the number of elements, `clear()` removes all elements, and `insert()` allows inserting elements at any position.
• **Convenience:** These methods encapsulate common operations, saving time and effort by eliminating the need to manage memory or create complex algorithms from scratch.
• **Reliability:** Using STL methods ensures that operations are bound by the same rules, providing consistency across an application.

Mastering STL methods provides a solid foundation for any C++ programmer, enabling the creation of efficient and high-quality applications.