## Add 2 and 2
2 + 2[1] 4Comments
Reading
This is a short one. The comment character in R is #. Each commented line must be preceded by a # symbol. There are no block comments in R. Comments are not evaluated when you run your code. R simply ignores anything after a # on a given line.
Do: run the following R code to generate two integer vectors and print the results.
Predict: what do you expect to happen if you put a # in front of the first line below, then run the code?
Explain: in the code above, the expression 1:10 is “commented out”, so R doesn’t evaluate that line at all. Instead, it’s treated as plain text, not code. So, running the code only prints the second vector, 2:8.
Comments are mainly useful for leaving short notes to yourself (or to anyone else reading your code) about why a particular line does what it does. You’ve already seen several examples of this throughout this module, e.g.:
Quick Check
What will the following code print? Predict first, then check your answer in the editor.
5 + 5
# 5 - 5
5 * 5