finsih most of the chapter

Author: Lukas Werner

ch3/basename1/basename.go

@@ -0,0 +1,23 @@
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println(basename("a/b/c.go"))
+}
+
+func basename(s string) string {
+	for i := len(s) - 1; i >= 0; i-- {
+		if s[i] == '/' {
+			s = s[i+1:]
+			break
+		}
+	}
+	for i := len(s) - 1; i >= 0; i-- {
+		if s[i] == '.' {
+			s = s[:i]
+			break
+		}
+	}
+	return s
+}

ch3/basename2/basename.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func main() {
+	fmt.Println(basename("a/b/c.go"))
+}
+
+func basename(s string) string {
+	slash := strings.LastIndex(s, "/")
+	s = s[slash+1:]
+	if dot := strings.LastIndex(s, "."); dot >= 0 {
+		s = s[:dot]
+	}
+	return s
+}

ch3/comma/comma.go

@@ -0,0 +1,17 @@
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println(comma("1234567890"))
+}
+
+func comma(s string) string {
+	n := len(s)
+	if n <= 3 {
+		return s
+	}
+	return comma(s[:n-3]) + "," + s[n-3:]
+}

ch3/mandelbrot/mandelbrot.go

@@ -2,15 +2,45 @@
 
 package main
 
-import "image"
+import (
+	"image"
+	"image/color"
+	"image/png"
+	"math/cmplx"
+	"os"
+)
 
 func main() {
+	f, err := os.Create("out.png")
+	if err != nil {
+		os.Exit(1)
+	}
 	const (
 		xmin, ymin, xmax, ymax = -2, -2, +2, +2
 		width, height          = 1024, 1024
 	)
 	img := image.NewRGBA(image.Rect(0, 0, width, height))
 	for py := 0; py < height; py++ {
-		y := float64(py) / height * (ymax)
+		y := float64(py)/height*(ymax-ymin) + ymin
+		for px := 0; px < width; px++ {
+			x := float64(px)/width*(xmax-xmin) + xmin
+			z := complex(x, y)
+			img.Set(px, py, mandelbrot(z))
+		}
+	}
+	png.Encode(f, img)
+	f.Close()
+}
+
+func mandelbrot(z complex128) color.Color {
+	const iterations = 200
+	const contrast = 15
+	var v complex128
+	for n := uint8(0); n < iterations; n++ {
+		v = v*v + z
+		if cmplx.Abs(v) > 2 {
+			return color.Gray{255 - contrast*n}
+		}
 	}
+	return color.Black
 }

ch3/mandelbrot/out.png

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"bytes"
+	"fmt"
+)
+
+func main() {
+	fmt.Println(intsToString([]int{1, 2, 3}))
+}
+
+func intsToString(values []int) string {
+	var buf bytes.Buffer
+	buf.WriteByte('[')
+	for i, v := range values {
+		if i > 0 {
+			buf.WriteString(", ")
+		}
+		fmt.Fprintf(&buf, "%d", v)
+	}
+	buf.WriteByte(']')
+	return buf.String()
+}