More Vectors

Let’s look at some more ways we can work with vectors.

Initializing

We can initialize a vector when we declare it. The following creates a vector with 5 elements, all initialized to 0:

std::vector<double> container(5, 0.0);

Notice that we are using () here instead of {}. As we’ll see later, this means that we are calling a function here to do the initialization (the constructor).

Here we instead initialize a vector by telling it the values of each of the elements:

std::vector<double> container2{10.0, 20.0, 30.0};

Size

As we saw earlier, we can always get the number of elements in a vector via the size() function:

std::vector<int> int_vec{1, 2, 3, 4, 5};

int nlen = int_vec.size();

Note

size() technically returns a value of type std::size_t, and here we implicitly cast it to an int. We learn more about casting later.

try it…

We saw that we access an element via []. What happens if we access the vector out of bounds?