## Exercise: Loops and Functions

``````package main

import (
"fmt"
"math"
)

func Sqrt(x float64) float64 {
z := 1.0
for i := 1; i < 10; i++ {
z -= (z*z - x) / (2*z)
}
return z
}

func main() {
fmt.Println(Sqrt(2))
fmt.Println(math.Sqrt(2))
}``````

## Exercise: Slices

``````package main

import "golang.org/x/tour/pic"

func Pic(dx, dy int) [][]uint8 {
pixels := make([][]uint8, dy)
for y := 0; y < dy; y++ {
pixels[y] = make([]uint8, dx)
for x := 0; x < dx; x++ {
pixels[y][x] = uint8(x^y)
}
}
return pixels
}

func main() {
pic.Show(Pic)
}``````

## Exercise: Fibonacci closure

``````package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
a, b := -1, 1

return func() int {
a, b = b, a + b

return b
}
}

func main() {
f := fibonacci()
for i := 0; i < 10; i++ {
fmt.Println(f())
}
}``````

## Exercise: Stringers

``````package main

import "fmt"

func(ip IPAddr) String() string {
return fmt.Sprintf("%v.%v.%v.%v", ip[0], ip[1], ip[2], ip[3])
}

func main() {
"loopback":  {127, 0, 0, 1},
"googleDNS": {8, 8, 8, 8},
}
for name, ip := range hosts {
fmt.Printf("%v: %v\n", name, ip)
}
}``````

## Exercise: Errors

``````package main

import (
"fmt"
)

type ErrNegativeSqrt float64

func (e ErrNegativeSqrt) Error() string {
return fmt.Sprintf("cannot Sqrt negative number: %v", float64(e))
}

func Sqrt(x float64) (float64, error) {
switch {
case x < 0:
return 0, ErrNegativeSqrt(x)
default:
z := 1.0
for i := 1; i < 10; i++ {
z -= (z*z - x) / (2*z)
}
return z, nil
}
}

func main() {
fmt.Println(Sqrt(2))
fmt.Println(Sqrt(-2))
}``````

``````package main

func (MyReader) Read(b []byte) (n int, err error) {
b[0] = 'A';
return 1, nil;
}

func main() {
}``````

``````package main

import (
"io"
"os"
"strings"
)

type rot13Reader struct {
}

for i := 0; i <= n; i++ {
bytes[i] = rot13(bytes[i])
}
return n, err
}

func rot13(b byte) byte {
if 'A' <= b && b <= 'Z' {
b = b + 13
if (b > 'Z') {
return b - 26
}
}

if 'a' <= b && b <= 'z' {
b = b + 13
if (b > 'z') {
return b - 26
}
}

return b
}

func main() {
s := strings.NewReader("Lbh penpxrq gur pbqr!")
io.Copy(os.Stdout, &r)
}``````

## Exercise: Images

``````package main

import "image"
import "image/color"
import "golang.org/x/tour/pic"

type Image struct {
width, height int
color uint8
opacity uint8
}

func (img *Image) Bounds() image.Rectangle {
return image.Rect(0, 0, img.width, img.height)
}

func (img *Image) ColorModel() color.Model {
return color.RGBAModel
}

func (img *Image) At(x, y int) color.Color {
return color.RGBA{uint8(x^y), uint8(x^y), img.color, img.opacity}
}

func main() {
m := Image{512, 512, 255, 255}
pic.ShowImage(&m)
}``````

## Exercise: Equivalent Binary Trees

``````package main

import "fmt"
import "golang.org/x/tour/tree"

// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk2(t *tree.Tree, ch chan int) {

}

func Walk(t *tree.Tree, ch chan int) {
walkRecur(t, ch)
close(ch)
}

func walkRecur(t *tree.Tree, ch chan int) {
if t.Left != nil {
walkRecur(t.Left, ch)
}

ch <- t.Value

if t.Right != nil {
walkRecur(t.Right, ch)
}
}

// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool {
ch1, ch2 := make(chan int), make(chan int)
go Walk(t1, ch1)
go Walk(t2, ch2)
for i := range ch1 {
if i != <-ch2 {
return false
}
}
return true
}

func main() {
ch := make(chan int)
go Walk(tree.New(1), ch)
for i := range ch {
fmt.Println(i)
}
fmt.Println(Same(tree.New(1), tree.New(1)))
fmt.Println(Same(tree.New(1), tree.New(2)))
}``````

## Exercise: Web Crawler

``````package main

import (
"fmt"
)

type Fetcher interface {
// Fetch returns the body of URL and
// a slice of URLs found on that page.
Fetch(url string) (body string, urls []string, err error)
}

// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher, foundURLs map[string]bool) {
// TODO: Fetch URLs in parallel.
// TODO: Don't fetch the same URL twice.
// This implementation doesn't do either:
if depth <= 0 {
return
}
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
foundURLs[url] = false
return
}
fmt.Printf("found: %s %q\n", url, body)
foundURLs[url] = true
for _, u := range urls {
Crawl(u, depth-1, fetcher, foundURLs)
}
return
}

func main() {
foundURLs := make(map[string]bool)
Crawl("https://golang.org/", 4, fetcher, foundURLs)
for url, success := range foundURLs {fmt.Println(url, success)}
}

// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult

type fakeResult struct {
body string
urls []string
}

func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}

// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"https://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"https://golang.org/pkg/",
"https://golang.org/cmd/",
},
},
"https://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"https://golang.org/",
"https://golang.org/cmd/",
"https://golang.org/pkg/fmt/",
"https://golang.org/pkg/os/",
},
},
"https://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"https://golang.org/",
"https://golang.org/pkg/",
},
},
"https://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"https://golang.org/",
"https://golang.org/pkg/",
},
},
}``````

1,647 total views,  1 views today

## Hello, Iris Go

Install Go & Iris

``````brew install go
go get -u github.com/kataras/iris``````

Create working directory & main.go

``````mkdir \$GOPATH/src/gowork
cd \$GOPATH/src/gowork
touch main.go``````
``````package main

import (
"github.com/kataras/iris"

"github.com/kataras/iris/middleware/logger"
"github.com/kataras/iris/middleware/recover"
)

func main() {
app := iris.New()
app.Logger().SetLevel("debug")
// Optionally, add two built'n handlers
// that can recover from any http-relative panics
// and log the requests to the terminal.
app.Use(recover.New())
app.Use(logger.New())

// Method:   GET
// Resource: http://localhost:8080/hello
app.Get("/hello", func(ctx iris.Context) {
ctx.JSON(iris.Map{"message": "Hello, Iris Go!"})
})

``````go run main.go