Arrays

An array holds a fixed number of values of the same type. Its length is part of its type, so [3]int and [4]int are different types.

Declare an array with a length in brackets, for example var scores [3]int. Each element initially has the zero value of its type. An array literal such as [3]int{10, 20, 30} supplies values, and [...]int{...} lets the compiler count them.

Arrays are values in Go. Assigning an array to another array of the same type copies its elements; the two arrays are then independent. For resizable sequences, Go programmers generally use slices instead.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import "fmt"

func main() {
	scores := [3]int{10, 20, 30}
	duplicate := scores
	duplicate[0] = 99
	fmt.Println("Original:", scores)
	fmt.Println("Copy:", duplicate)
	fmt.Println("Length:", len(scores))
}

Output

Original: [10 20 30]
Copy: [99 20 30]
Length: 3

The array literal creates three integers. Assigning to duplicate copies the entire array. Updating duplicate[0] changes only the copy, while len(scores) remains 3 because an array has a fixed length.

• An array length is part of its type; [3]int is not interchangeable with [4]int.
• Arrays are copied on assignment, unlike the element-sharing behavior of slices.

Create a [4]string array of weekdays. Assign it to another variable, change one element and compare the arrays.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Go Arrays in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.