Question

What is the output of the following C++ code? vector classList; classList.push_back("Nisha"); classList.push_back("Tony"); classList.push_back("Bobby"); classList.push_back("Peter"); for (unsigned int i = 0; i < classList.size(); i++) cout << classList[i] << " "; cout << endl;

Short answer

The output is: Nisha Tony Bobby Peter.

Step-by-step solution

Initialize the vector

A `vector` named `classList` is declared and initialized as an empty vector of strings. This vector will store the names of class members.

Add elements to the vector

The `push_back` function is used to add the strings "Nisha", "Tony", "Bobby", and "Peter" to the `classList` vector one by one. After this step, the vector contains four elements.

Iterate over the vector with a for loop

A `for` loop is set up to iterate over `classList`. The loop starts with `i = 0` and continues while `i` is less than `classList.size()`, meaning it will run four times (once for each name in the vector).

Output each element with cout

Inside the loop, `cout` is used to print each element of the `classList`. The element at index `i` will be printed followed by a space. As a result, each name in the vector will be printed in sequence, separated by spaces.

Print new line after loop

After the loop completes, `cout << endl;` ensures the output is followed by a newline, marking the end of the output.

Key concepts

vector initialization

In C++, vectors are a part of the Standard Template Library (STL) and are used to store elements dynamically. They offer flexibility compared to arrays as they can change size during runtime. To initialize a vector, you simply declare it with a specific type.

For example, the line `vector classList;` initializes `classList` as a vector of strings. This means that you can store multiple string elements in this vector, such as names or phrases. At the time of declaration, `classList` is empty, meaning it doesn't contain any elements yet.

Using vectors can be beneficial because:

• They automatically manage memory, so there's no need to worry about manual memory allocation and deallocation.
• They have built-in functions that make manipulation of the data easier.
• They can grow and shrink as necessary, adapting to the data you need to store.

Understanding vector initialization is crucial, as it sets the foundation for performing further operations like adding, removing, and accessing elements.

push_back function

The `push_back` function is a valuable part of the C++ vector operations. It's used to add elements to the end of a vector. This function automatically handles resizing the vector if necessary, so you don't need to adjust any size manually.

In our example, `classList.push_back("Nisha");` adds the string "Nisha" to the end of the `classList` vector. This operation is repeated for "Tony", "Bobby", and "Peter", each call to `push_back` appending a new name.

Here are some key points about using `push_back`:

• It extends the size of the vector by one, and the new slot is filled with the specified value.
• It is efficient, but be mindful of the overhead from resizing, especially in very large datasets.
• It simplifies adding data without requiring knowledge of the current number of elements.

This function is central when dealing with vectors, as it facilitates dynamic growth of the data you're managing.

for loop iteration

Iterating through elements in a vector is commonly done using a `for` loop. This allows you to access each element sequentially, making it ideal for operations that process or display all elements.

In the given code, the loop `for (unsigned int i = 0; i < classList.size(); i++)` starts with `i = 0`, continues as long as `i` is less than the number of elements, and increments `i` by one in each step. This setup is known as a **count-controlled loop**, where the loop runs a fixed number of times based on the condition specified.

Important aspects of using a `for` loop with vectors include:

• You can iterate through all elements efficiently from the first to the last.
• The vector's `size()` function dynamically retrieves the current number of elements, which is crucial for reliable iteration—especially when handling changes during runtime.
• The index `i` provides direct access to each element within the loop body.

This type of loop is widely applicable in programming, making it a fundamental skill in processing lists of data.

cout function

The `cout` function, from the `` library in C++, is essential for printing output to the console. It's often used to display information to users or for debugging purposes.

In our exercise, `cout` is combined with `<<` to output each name in the `classList` vector. The loop iterates through each element, with each `cout << classList[i] << " "` statement printing the current element followed by a space.

Here's why `cout` is important:

• It is simple and intuitive for displaying strings, numbers, and more complex objects by overloading the operator.
• It integrates seamlessly with loops to print multiple pieces of data or process them in real-time.
• Its use of operators like `<<` allows for concatenating different data types within a single output statement.

Mastering `cout` and its formatting capabilities is a core part of C++ programming, enabling clear communication of your program's output.