Variables in Go

Flavio CopesOctober 19, 2022About 2 min

Variables in Go 관련

The Go Handbook – Learn Golang for Beginners

Golang is an awesome, simple, modern, and fast programming language. It’s compiled, open source, and strongly typed. Golang – also called Go – was created by Google engineers with these main goals: make their projects compile (and run) faster be sim...

The Go Handbook – Learn Golang for Beginners

One of the first things you do in a programming language is defining a variable.

In Go we define variables using var:

var age = 20

You can define variables at the package level:

package main

import "fmt"

var age = 20

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

or inside a function:

package main

import "fmt"

func main() {
    var age = 20

    fmt.Println("Hello, World!")
}

Defined at the package level, a variable is visible across all the files that compose the package. A package can be composed of multiple files, you just need to create another file and use the same package name at the top.

Defined at the function level, a variable is visible only within that function. It’s initialized when the function is called, and destroyed when the function ends the execution.

In the example we used:

var age = 20

we assign the value 20 to age.

This makes Go determine that the type of the variable age is int.

We’ll see more about types later, but you should know there are many different ones, starting with int, string, and bool.

We can also declare a variable without an existing value, but in this case we must set the type like this:

var age int
var name string
var done bool

When you know the value, you typically use the short variable declaration with the := operator:

age := 10
name := "Roger"

For the name of the variable you can use letters, digits, and the underscore _ as long as the name starts with a character or _.

Names are case sensitive.

If the name is long, it’s common to use camelCase. So to indicate the name of the car we use carName.

You can assign a new value to a variable with the assignment operator =

var age int
age = 10
age = 11

If you have a variable that never changes during the program you can declare it as a constant using const:

const age = 10

You can declare multiple variables on a single line:

var age, name

and initialize them too:

var age, name = 10, "Roger"

//or

age, name := 10, "Roger"

Declared variables that are not used in the program raise an error and the program does not compile.

You will see a warning in VS Code:

and the error from the compiler:

Error in compiler for unused declared variables

If you declare a variable without initializing it to a value, it is assigned a value automatically that depends on the type – for example an integer is 0 and a string is an empty string.