Comments are not executed in R, start with the character # and end with the end of the line.

Input:

source_code/appendix_b_r/example01_comments.r
print("This text is printed because the print statement is executed")
#This is just a comment and will not be executed.
#print("Even commented statements are not executed.")
print("But the comment finished with the end of the line.")
print("So the 4th and 5th line of the code are executed again.")

Output:

$ Rscript example01_comments.r 
[1] "This text will be printed because the print statemnt is executed"
[1] "But the comment finished with the end of the line."
[1] "So the 4th and 5th line of the code are executed again."