Complex numbers are related to calculus and advanced math and widely used in quantum mechanics, signals processing, and physics.

Since this course aims to teach R basics, we will not dig deep into this subject but only consider this as one of the numerical types. Each complex number consists of *real* (let it be `a`) and *imaginary* (let it be `b`). Then the expression `a+bi` is called a complex number. `i` - is an imaginary unit such that `i^2 = -1`.

To create such a number in R, use the same denotation as above: `a + bi`. For example, we can create a complex number with the real part `5` and the imaginary part `-3`.

compl = 5 - 3i # Creating complex number
compl # Output the number
typeof(compl) # Output its type

The output is:
```
[1] 5-3i
[1] "complex"
```

You can perform arithmetic operations learned before with all the number types we have learned in this section.

The result has a `"complex"` type since the complex numbers are an extension field of the real numbers (and integers, respectively).

In the first section, you will consider the very basics of R - outputting and performing basic operations. You will finish the section with the variables theory.

In the second section, you will learn the vector class in R, which represents single values too. You will consider the main data types for single values and how to work with multiple values of a kind at once.

Factors (or categorical variables) are widely used in real life. These are blood types, currencies, nationalities, brands, etc. Unlike numerical variables, factors are limited to a finite number of values.