Go Basics

Go Variables and Constants: var, := and const

Two ways to declare a variable, what a zero value is, and values that never change.

Beginner
2 min read
1 runnable example

What you'll learn

var and :=
Zero values
const

Run code →

Declaration → result

var year int0, the zero value

score := 10int, inferred

const MaxScore = 100cannot change

Declare, then use

Go has two ways to create a variable. var names the type, and := lets Go work out the type from the value. A variable that is declared without a value gets a zero value such as 0 or an empty string.

year is declared without a value, so it starts at 0 until 2009 is assigned. := can only be used inside a function and can declare several variables at once. A const cannot be changed after it is declared.

Key points

var names the type; := infers it.
A variable without a value starts at its zero value.
A const cannot change.

Runnable Go example

Run code →

main.go

package main

import "fmt"

const MaxScore = 100

func main() {
	var language string = "Go"
	var year int // zero value: 0
	score := 10  // short declaration, type inferred
	score += 5
	year = 2009

	name, version := "gopher", 1.21
	fmt.Println(language, year, score, MaxScore)
	fmt.Println(name, version)
}

Get a Run button for this example Result of running the code

Go 2009 15 100
gopher 1.21

Practice

Open the example in the online compiler, change a value or add a line, and predict the output before you run it. Then break the code on purpose and read the compiler's message.

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