Collections and Composite Types

Arrays

Go arrays store a fixed number of values of the same type.

array An array type includes its length, such as `[3]int`.

Arrays

index
arrays_intro.go
Replay: real traced execution (multi-file project)
package main

import "fmt"

func main() {
	var index = 1
	numbers := [3]int{4, 7, 9}
	value := numbers[index]

	fmt.Println("numbers=", numbers)
	fmt.Println("index=", index)
	fmt.Println("value=", value)
}

package main

import "fmt"

func main() {
	var index = 0
	numbers := [3]int{4, 7, 9}
	value := numbers[index]

	fmt.Println("numbers=", numbers)
	fmt.Println("index=", index)
	fmt.Println("value=", value)
}

package main

import "fmt"

func main() {
	var index = 2
	numbers := [3]int{4, 7, 9}
	value := numbers[index]

	fmt.Println("numbers=", numbers)
	fmt.Println("index=", index)
	fmt.Println("value=", value)
}

  1. index ← 1, numbers ← [3]int{4, 7, 9}, value ← 7

    5func main() {6  var index→ 1 = 1 //@index=0, 27  numbers→ [3]int{4, 7, 9} := [3]int{4, 7, 9}8  value→ 7 := numbers[index]7910  fmt.Println("numbers=", numbers[3]int{4, 7, 9})11  fmt.Println("index=", index1)12  fmt.Println("value=", value7)13}
    outputnumbers= [4 7 9]
index= 1
value= 7

  1. index ← 0, numbers ← [3]int{4, 7, 9}, value ← 4

    5func main() {6  var index→ 0 = 07  numbers→ [3]int{4, 7, 9} := [3]int{4, 7, 9}8  value→ 4 := numbers[index]4910  fmt.Println("numbers=", numbers[3]int{4, 7, 9})11  fmt.Println("index=", index0)12  fmt.Println("value=", value4)13}
    outputnumbers= [4 7 9]
index= 0
value= 4

  1. index ← 2, numbers ← [3]int{4, 7, 9}, value ← 9

    5func main() {6  var index→ 2 = 27  numbers→ [3]int{4, 7, 9} := [3]int{4, 7, 9}8  value→ 9 := numbers[index]9910  fmt.Println("numbers=", numbers[3]int{4, 7, 9})11  fmt.Println("index=", index2)12  fmt.Println("value=", value9)13}
    outputnumbers= [4 7 9]
index= 2
value= 9

Pick by Index

  1. numbers stores three values: 4, 7, and 9.
  2. Go array indexes start at 0.
  3. index is 1.
  4. numbers[index] reads 7. | Index | Value | Selected? | | --- | --- | --- | | 0 | 4 | no | | 1 | 7 | yes | | 2 | 9 | no |

Exercise: arrays_intro.go

Read one array value by index and print the array, index, and selected value