meet it

Every item has a number, starting from 0.

Each item has a position number called its . Go starts counting at 0, so snacks[0] is the first item and snacks[1] is the second. The last one is snacks[len(snacks)-1].

Change an item by putting a new value at its index: snacks[1] = "pear". Ask for an index that does not exist, and the program crashes with a .

adds an item to the end. It hands back a longer slice, so store it: snacks = append(snacks, "grapes").

package main
import "fmt"
func main() {
	snacks := []string{"crisps", "apple", "cake"}
	fmt.Println(snacks[0])
	snacks[1] = "pear"
	snacks = append(snacks, "grapes")
	fmt.Println(snacks)
	fmt.Println(snacks[len(snacks)-1])
}

A panic happens while the program runs, so lines before it still show their output.

guess first

Swap one, add one. What will this show?

Guess before you run it. Wrong guesses are how you learn, and nothing is marked.

package main
import "fmt"
func main() {
	pets := []string{"cat", "dog", "fish"}
	pets[0] = "hamster"
	pets = append(pets, "parrot")
	fmt.Println(pets[0], len(pets))
}

your turn

Your turn. Join the queue.

Type your own name to join the end of the queue. Index 2 is the third item, which is you.

Your code

output

press run to see what happens

fix it

This program panics. Can you fix it?

Broken code to fix

output

press run to see what happens

There are 3 colours. What index does the first one have?
Counting starts at 0, so the indexes are 0, 1 and 2. There is no index 3.
Change colours[3] to colours[2], then press run.

nailed it

you can reach into a slice now. :D

Indexes start at 0, so the first item is [0].
s = append(s, item) adds an item to the end.
A missing index makes the program panic.

new words in your collection

index
panic
append

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