a-tour-of-go

exercise-errors.go

package main

import (
	"fmt"
)

type ErrNegativeSqrt float64

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

func Sqrt(x float64) (float64, error) {
	
	if x < 0 {
		return 0, ErrNegativeSqrt(x)
	}
	
	z := 0.0
	for i := 0; i < 10; i++ {
		z = x - (x * x - 2) / (2 * x)
		x = z
	}
	return z, nil
}

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

exercise-fibonacci-closure.go

package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
	a := 0
	b := 1
	c := 0
	x := 0
	
	return func() int {
		switch x {
		case 0:
			x++
			return a
		case 1:
			x++
			return b
		default:
			x++
			c = a + b
			a = b
			b = c
			return c
		}
	}
}

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

exercise-loops-and-functions.go

package main

import (
	"fmt"
	"math"
)

func Sqrt(x float64) float64 {
	z := 0.0
	for i := 0; i < 10; i++ {
		z = x - (x * x - 2) / (2 * x)
		x = z
	}
	return z
}

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

exercise-maps.go

package main

import (
	"golang.org/x/tour/wc"
	"strings"
)

func WordCount(s string) map[string]int {
	f := strings.Fields(s)
	m := make(map[string]int)
	
	for i, v := range f {
		if f[i] == v {
			m[v] += 1
		}
	}
	
	return m
}

func main() {
	wc.Test(WordCount)
}

exercise-reader.go

package main

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

type MyReader struct{}

// TODO: Add a Read([]byte) (int, error) method to MyReader.
func (r MyReader) Read(b []byte) (int, error) {
	for i := 0; i < len(b); i++ {
		b[i] = 'A'
	}
	return len(b), nil
}

func main() {
	reader.Validate(MyReader{})
}

exercise-slices.go

package main

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

func Pic(dx, dy int) [][]uint8 {
	pic := make([][]uint8, dy)
	for y := 0; y < dy; y++ {
		pic[y] = make([]uint8, dx)
		for x := 0; x < dx; x++ {
			pic[y][x] = uint8((x+y)/2)
		}
	}
	return pic
}

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

exercise-stringer.go

package main

import "fmt"

type IPAddr [4]byte

// TODO: Add a "String() string" method to IPAddr.
func (ipAddr IPAddr) String() string {
	return fmt.Sprintf("%v.%v.%v.%v", ipAddr[0], ipAddr[1], ipAddr[2], ipAddr[3])
}

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