Gopl 练习题题解

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字数统计: 889 字

说明

本文解答GOPL的主要练习题

第一章

1.5 李萨如图形改颜色

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package main

import (
	"image"
	"image/color"
	"image/gif"
	"io"
	"math"
	"math/rand"
	"os"
)

//!+main

var palette = []color.Color{color.Black, color.RGBA{0x00,0xff,0x00,0xff}}

const (
	blackIndex = 0 // first color in palette
	greenIndex = 1 // next color in palette
)

func main() {
	//!-main
	// The sequence of images is deterministic unless we seed
	// the pseudo-random number generator using the current time.
	// Thanks to Randall McPherson for pointing out the omission.
	rand.Seed(time.Now().UTC().UnixNano())

	if len(os.Args) > 1 && os.Args[1] == "web" {
		//!+http
		handler := func(w http.ResponseWriter, r *http.Request) {
			lissajous(w)
		}
		http.HandleFunc("/", handler)
		//!-http
		log.Fatal(http.ListenAndServe("localhost:8000", nil))
		return
	}
	//!+main
	lissajous(os.Stdout)
}

func lissajous(out io.Writer) {
	const (
		cycles  = 5     // number of complete x oscillator revolutions
		res     = 0.001 // angular resolution
		size    = 100   // image canvas covers [-size..+size]
		nframes = 64    // number of animation frames
		delay   = 8     // delay between frames in 10ms units
	)
	freq := rand.Float64() * 3.0 // relative frequency of y oscillator
	anim := gif.GIF{LoopCount: nframes}
	phase := 0.0 // phase difference
	for i := 0; i < nframes; i++ {
		rect := image.Rect(0, 0, 2*size+1, 2*size+1)
		img := image.NewPaletted(rect, palette)
		for t := 0.0; t < cycles*2*math.Pi; t += res {
			x := math.Sin(t)
			y := math.Sin(t*freq + phase)
			img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5),
				greenIndex)
		}
		phase += 0.1
		anim.Delay = append(anim.Delay, delay)
		anim.Image = append(anim.Image, img)
	}
	gif.EncodeAll(out, &anim) // NOTE: ignoring encoding errors
}

//!-main

1.6 李萨如图形多彩颜色

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package main

import (
	"image"
	"image/color"
	"image/gif"
	"io"
	"log"
	"math"
	"math/rand"
	"net/http"
	"os"
)

var palette = []color.Color{
	color.Black,
	color.White,
	color.RGBA{0x00, 0xff, 0x00, 0xff},
	color.RGBA{0xff, 0x00, 0x00, 0xff},
	color.RGBA{0x00, 0xff, 0xff, 0xff},
	color.RGBA{0x0f, 0xff, 0x07, 0xff},
	color.RGBA{0xf0, 0xf8, 0x09, 0xff},
	color.RGBA{0x09, 0xfa, 0xcb, 0xff},
	color.RGBA{0x0b, 0xb7, 0xb9, 0xff},
	color.RGBA{0xc5, 0xa1, 0xb2, 0xff},
}

func main(){
	if len(os.Args)>1 && os.Args[1] == "web"{
		handler := func(w http.ResponseWriter,r *http.Request){
			lissajous(w)
		}
		http.HandleFunc("/",handler)
		log.Fatal(http.ListenAndServe("localhost:8000",nil))
	}
	file, _:= os.Create("1.gif")
	lissajous(file)
	file.Close()
}
func lissajous(out io.Writer) {
	const (
		cycles  = 5     // number of complete x oscillator revolutions
		res     = 0.001 // angular resolution
		size    = 100   // image canvas covers [-size..+size]
		nframes = 64    // number of animation frames
		delay   = 8     // delay between frames in 10ms units
	)
	freq := rand.Float64() * 3.0 // relative frequency of y oscillator
	anim := gif.GIF{LoopCount: nframes}
	phase := 0.0 // phase difference
	for i := 0; i < nframes; i++ {
		rect := image.Rect(0, 0, 2*size+1, 2*size+1)
		img := image.NewPaletted(rect, palette)
		colorIndex := uint8(rand.Intn(10))
		for t := 0.0; t < cycles*2*math.Pi; t += res {
			x := math.Sin(t)
			y := math.Sin(t*freq + phase)
			img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5),
			colorIndex)
		}
		phase += 0.1
		anim.Delay = append(anim.Delay, delay)
		anim.Image = append(anim.Image, img)
	}
	gif.EncodeAll(out, &anim) // NOTE: ignoring encoding errors
}

1.7 io.Copy(dst,src)

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func main(){
	for _, url := range os.Args[1:]{
		resp,_ := http.Get(url)
		//body,_ :=ioutil.ReadAll(resp.Body)
		_,err := io.Copy(os.Stdout,resp.Body)
		if err!= nil{fmt.Fprintln(os.Stderr,"copy error")}
		resp.Body.Close()
		//fmt.Printf("%s",body)
	}
}

1.8 fetch加http://前缀

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func main(){
	for _, url := range os.Args[1:]{
		if !strings.HasPrefix(url,"http://"){
			url = "http://" + url
		}
		resp,_ := http.Get(url)
		body,_ :=ioutil.ReadAll(resp.Body)
		resp.Body.Close()
		fmt.Printf("%s",body)
	}
}

1.9 fetch 输出HTTP状态

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func main(){
	for _, url := range os.Args[1:]{
		if !strings.HasPrefix(url,"http://"){
			url = "http://" + url
		}
		resp,err := http.Get(url)
		if err!=nil{
			fmt.Fprintf(os.Stderr,"fetch: %v\n",err)
		}
		fmt.Println("HTTP Status:",resp.Status)
		body,err :=ioutil.ReadAll(resp.Body)
		if err!=nil{
			fmt.Fprintf(os.Stderr,"fetch:reading %s:%v\n",url,err)
		}
		resp.Body.Close()
		fmt.Printf("%s",body)
	}
}