Three new books, Go Optimizations 101, Go Details & Tips 101 and Go Generics 101 are published now. It is most cost-effective to buy all of them through this book bundle in the Leanpub book store.

loop 4

What does the following program print?

package main

func main() {
	i, s := 9, []int{}
	
	for i = range s {}
	print(i)
	
	for i = 0; i < len(s); i++ {}
	print(i)

	s = append(s, 1, 2, 3, 4, 5)
	
	for i = range s {}
	print(i)
	
	for i = 0; i < len(s); i++ {}
	println(i)
}

Choices:

0055
9055
9045
0045

Answer: 9045

Run it on Go play.

Key point:

A for-range loop never set the first iteration variable to an invalid index.

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Tapir, the author of Go 101, has been on writing the Go 101 series books and maintaining the go101.org website since 2016 July. New contents will be continually added to the book and the website from time to time. Tapir is also an indie game developer. You can also support Go 101 by playing Tapir's games (made for both Android and iPhone/iPad):

Color Infection (★★★★★), a physics based original casual puzzle game. 140+ levels.
Rectangle Pushers (★★★★★), an original casual puzzle game. Two modes, 104+ levels.
Let's Play With Particles, a casual action original game. Three mini games are included.

Individual donations via PayPal are also welcome.

Articles in this book:

slice: 1, 2, 3
map: 1
channel: 1
loop: 1, 2, 3, 4
switch: 1
defer: 1, 2
panic/recover: 1, 2
reflect: 1, 2
const: 1, 2, 3, 4
operator: 1, 2, 3
function call: 1
scope: 1, 2
nil: 1
embedding: 1

(more are coming ...)