Question

What do the following statements do? a. vector list(50); b. vector nameList;

Short answer

Statement a initializes a vector of 50 zero integers; statement b initializes an empty vector of strings.

Step-by-step solution

Analyzing Statement a

The statement `vector list(50);` creates a vector named `list` that can hold `int` types. The number `50` inside the parentheses indicates that the vector is initialized to have 50 elements, each set to the default value of an integer, which is 0.

Analyzing Statement b

The statement `vector nameList;` creates a vector named `nameList` that can hold `string` types. However, in this case, no number is provided, so `nameList` is initialized as an empty vector without any elements upon creation.

Key concepts

vector

In C++, the vector is a versatile container that can grow or shrink dynamically. When we use a declaration like `vector list(50);`, here's what's happening:

• The `vector` syntax specifies that the elements of this vector are of the integer type, allowing the storage of different integer values.
• The `list` is the name given to this specific vector instance.
• The `(50)` indicates that the vector should be initialized with 50 elements right from the get-go.

A unique aspect of vectors is their dynamic nature. Although `list` starts with 50 elements, you can add or remove items as needed. This is especially helpful when you don't know in advance how many elements you'll need.

vector

Vectors can also be used to store other types of data, like strings. The declaration `vector nameList;` is a prime example:

• The `vector` tells us that this container will hold `string` type data, perfect for words or text-based information.
• It is initialized without a size parameter, resulting in an empty vector called `nameList` when it's created.

As such, `nameList` is perfectly set up to start receiving and managing strings dynamically. As with any vector, you can easily append new strings, remove them, or access them in various ways, which is incredibly useful when dealing with collections of text.

initialization of vectors

Initializing vectors in C++ can be done in several ways, providing flexibility based on the needs of your application:

• With predefined size: As seen in `vector list(50);`, this initializes the vector with a specified number of elements, all set to the default value of the type.
• Without predefined size: Declaring something like `vector nameList;` results in a dynamic, empty vector that's ready for elements to be added later.

These initializations allow vectors to be tailored initially to fit specific use cases—whether you're storing a preset number of elements or preparing an open-ended collection to which you will add later.

default values in vectors

Understanding default values for vector initialization is crucial for utilizing their flexibility effectively:

• Integers: For `vector list(50);`, each of the 50 integer elements is initialized to 0. This automatic zeroing ensures that you start with a consistent state.
• Strings and other types: For `vector nameList;`, because it's initialized empty, the vector naturally contains no elements until you decide to add them. When initialized with a size, elements are default-initialized, which for strings means they will be empty ("").

When working with vectors, these default settings provide a reliable baseline, allowing developers to focus on what to add or remove next without worrying about inconsistent or uninitialized states.