Go Comments

A comment is a note in code that the compiler ignores. Comments help people read and understand code.

A line comment

The comment sits on its own line. The print line below it still runs.

package main

import "fmt"

func main() {
	// Print a greeting
	fmt.Println("Hello")
}

A block comment around a statement

The block comment covers one whole statement. That statement does not run.

package main

import "fmt"

func main() {
	/* fmt.Println("Hidden") */
	fmt.Println("Visible")
}

A trailing comment

The comment follows code on the same line. The code still runs as usual.

package main

import "fmt"

func main() {
	fmt.Println("Done") // Mark the end
}

Example

package main

import "fmt"

func main() {
	// Print the plan for today
	fmt.Println("Plan for today")
	fmt.Println("Write one program") // The second line of the plan
}

Key points

Use // to start a line comment.
A line comment runs to the end of its line.
Use /* and */ to start and end a block comment.
A block comment can cover one statement or many lines.
A trailing comment sits on the same line as code.

In this example, a line comment sits above the first print line. The first line prints Plan for today. A trailing comment sits after the second print line. The second line prints Write one program.

Note

The compiler skips every comment when it builds a program.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Go Playground

package main

import "fmt"

func main() {
	// Print the plan for today
	fmt.Println("Plan for today")
	fmt.Println("Write one program") // The second line of the plan
}

Exercise

Which marks the start of a line comment?

// /* % #