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Go Output

Go output is the text and numbers a program prints to the screen. The fmt package gives three ways to print values.

Println ends each line

Each Println call prints one value. Each call ends its line.

package main

import "fmt"

func main() {
	fmt.Println("Hello")
	fmt.Println("World")
}

Print joins strings with no space

Println adds a space between two strings. Print joins two strings with no space.

package main

import "fmt"

func main() {
	fmt.Println("a", "b")
	fmt.Print("a", "b")
}

Print spaces two numbers

Neither value here is a string. Print puts a space between the two numbers.

package main

import "fmt"

func main() {
	fmt.Print(1, 2)
}

Printf fills in values

The pattern holds two verbs. Printf fills %s with a string and %d with a number.

package main

import "fmt"

func main() {
	fmt.Printf("%s is %d", "Hana", 27)
}

Printf shows a type and a value

The %T verb prints the type of a value. The %v verb prints the value itself.

package main

import "fmt"

func main() {
	fmt.Printf("%T %v", "Go", "Go")
}

Example

package main

import "fmt"

func main() {
	fmt.Printf("%s %d\n", "Pen", 3)
	fmt.Printf("%s %d", "Total", 6)
}

Key points

  • fmt.Println prints values and ends the line.
  • fmt.Print prints values without ending the line.
  • fmt.Print adds a space between two numbers.
  • fmt.Println adds spaces between the values it prints.
  • fmt.Printf builds a line from a pattern and values.
  • Use %d for a whole number and %s for a string.
  • Use %T for a type and %v for a value.

In this example, the first Printf prints Pen and the count 3. The newline ends the first line. The second Printf prints Total and the number 6.

Note

fmt.Printf adds no newline on its own.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Go Playground

Exercise

Which call prints a value and ends the line?