Go Arrays

An array keeps several values of one type together under a single name. That saves you from creating a separate variable for every value.

Declare an Array

Go lets you declare an array either with the var keyword or with the := operator.

The syntax here uses var:

Example

Here the length of each array is written out: 3 for arr1 and 5 for arr2. One uses var, the other :=:

Declare two arrays with defined size: one of strings with values, one of integers with values. Print both arrays.

> Output: Go program and captured output

Prompt

Declare two arrays with defined size: one of strings with values, one of integers with values. Print both arrays.

Output: Go program and captured output

package main
import ("fmt")

func main() {
  var arr1 = [3]int{1, 2, 3}
  arr2 := [5]int{4, 5, 6, 7, 8}

  fmt.Println(arr1)
  fmt.Println(arr2)
}

Example

Replace the length with ... and Go counts the values for you, so these two arrays end up with lengths 3 and 5:

Declare two arrays with inferred length using the ... syntax. Print both arrays.

> Output: Go program and captured output

Prompt

Declare two arrays with inferred length using the ... syntax. Print both arrays.

Output: Go program and captured output

package main
import ("fmt")

func main() {
  var arr1 = [...]int{1, 2, 3}
  arr2 := [...]int{4, 5, 6, 7, 8}

  fmt.Println(arr1)
  fmt.Println(arr2)
}

Syntax

When you state the length yourself:

var array_name = [length]datatype{values}

Syntax

When Go works out the length for you:

var array_name = [...]datatype{values}

Access Elements of an Array

To read one element of an array, write its index number in square brackets.

Counting begins at 0, not 1, so [0] gives you the first element, [1] the second, and so on.

Example

Indexes 0 and 2 give the first and third values of prices:

Declare an array of prices. Access the first and third elements by index.

> Output: Go program and captured output

Prompt

Declare an array of prices. Access the first and third elements by index.

Output: Go program and captured output

package main
import ("fmt")

func main() {
  prices := [3]int{10, 20, 30}

  fmt.Println(prices[0])
  fmt.Println(prices[2])
}

Change Elements of an Array

The same index notation works for writing: assign a new value to an index and that element is replaced.

Example

Assigning to prices[2] replaces the third value, 30, with 50:

Declare an array, change the third element, then print the first and third elements.

> Output: Go program and captured output

Prompt

Declare an array, change the third element, then print the first and third elements.

Output: Go program and captured output

package main
import ("fmt")

func main() {
  prices := [3]int{10, 20, 30}
  prices[2] = 50
  fmt.Println(prices[0])
  fmt.Println(prices[2])
}

Array Initialization

Any array element you leave without a value is not really empty. Go fills it with the default value of its type, and the same goes for an array you never initialize at all.

Note: For int that value is 0; for string it is "".

Example

You can set only the positions you care about by writing index:value. Here index 1 gets 10 and index 2 gets 40, while the other three elements stay at 0:

Declare an array of five integers where only some indexes are initialized. Print the array.

> Output: Go program and captured output

Prompt

Declare an array of five integers where only some indexes are initialized. Print the array.

Output: Go program and captured output

package main
import ("fmt")

func main() {
  arr1 := [5]int{1:10, 2:40}

  fmt.Println(arr1)
}

Find the Length of an Array

To learn how many elements an array has, pass it to the len() function.