Variables and types in Go

A variable in Go stores a typed value. You declare it either with the var keyword or, inside a function, with the short := operator. Go is statically typed, so every variable has a type that is fixed at compile time — but you rarely need to write that type yourself thanks to type inference.

Declaring a variable with var

The var keyword works everywhere: at package level and inside functions. You can give the type, the value, or both.

var name string = "Ada"
var count int = 3
var ready bool // no value: ready is false

When you provide an initial value, you can drop the type and let the compiler infer it:

var name = "Ada" // inferred as string
var pi = 3.14    // inferred as float64

The short declaration operator :=

Inside a function, := declares and initialises a variable in one step. It is the most common form in idiomatic Go.

package main

import "fmt"

func main() {
	name := "Ada"
	year := 1815
	fmt.Printf("%s was born in %d\n", name, year)
}

Zero values

If you declare a variable without a value, Go initialises it to the zero value of its type. There are no uninitialised variables in Go.

var total int       // 0
var label string    // ""
var enabled bool    // false

A complete example

The program below declares variables in several ways and prints them. It compiles and runs as-is.

package main

import "fmt"

func main() {
	// Explicit type.
	var language string = "Go"
	// Inferred type.
	version := 1.24
	// Zero value.
	var stars int

	stars = 42

	fmt.Printf("%s %.2f has %d stars\n", language, version, stars)
}

Running it prints:

Go 1.24 has 42 stars

Common mistakes

• Declaring a variable you never use. Go refuses to compile a program with an unused local variable. Remove it or use _ to discard a value.
• Using := at package level. Outside a function, only var is allowed.
• Re-declaring with :=. At least one variable on the left of := must be new; otherwise use = for a plain assignment.

Practice

Declare a variable celsius set to 100, compute fahrenheit with the formula celsius*9/5 + 32, and print 100°C = 212°F.

package main

import "fmt"

func main() {
	celsius := 100
	fahrenheit := celsius*9/5 + 32
	fmt.Printf("%d°C = %d°F\n", celsius, fahrenheit)
}

Summary

• Use var to declare variables anywhere; use := inside functions.
• Type inference lets you omit the type when you provide a value.
• Every variable has a zero value, so nothing is ever left uninitialised.

Next, learn how to make decisions with conditionals in Go, then how to group logic into functions.