Julia Comments

A comment is a note inside code that Julia ignores when the program runs. Comments help people who read the code later.

A single-line comment is ignored

The first line is a note for the reader. Only the second line runs.

# This line is a note
println("Hello")

A block comment spans several lines

The note between #= and =# covers two lines. Julia skips the whole note.

#=
This note spans
two lines.
=#
println("After the note")

A comment can follow a statement

The statement runs first on this line. The note after the # sign is ignored.

println("Visible") # This note is ignored

Example

# A program with two kinds of notes
println("First line")
#=
A longer note
about the next line.
=#
println("Second line")

Key points

Comment: a note inside code that Julia ignores.
Single-line comment: a comment that starts with # and runs to the end of the line.
Block comment: a comment that starts with #= and ends with =#.
Use a block comment for a note that spans several lines.
Placement: a comment can sit on its own line or after a statement on the same line.

In this example, the first line is a single-line comment, so Julia skips it. The first println prints First line. A block comment then spans three lines and is skipped, and the last println prints Second line.

Note

comments change nothing about what a program prints.

Try it Yourself

Edit the code, then press Run.

Running is simulated · JuliaHub

# A program with two kinds of notes
println("First line")
#=
A longer note
about the next line.
=#
println("Second line")

Exercise

Which symbol starts a single-line comment in Julia?

# // -- **