A Tour of Go

tour.go

//Cbrt.go
//Advanced Exercise: Complex cube roots

package main

import (
    "fmt"
    "math/cmplx"
    )

func Cbrt(x complex128) complex128 {
    var z complex128 = 1
    for i:= 1; i < 10; i++ {
        delta := (cmplx.Pow(z,3) - x)/(3 * cmplx.Pow(z,2))
        z = z - delta
    }
    return z
}

func main() {
    fmt.Println(Cbrt(2))
}

//Exercise: Errors

package main

import (
    "fmt"
)

type ErrNegativeSqrt float64

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


func Sqrt(f float64) (float64, error) {
    if f < 0 {
        return 0, ErrNegativeSqrt(f)
    }
    var z float64 = 1
    var delta float64
    for {
        delta = (z*z - f)/(2*z)
        z = z - delta
        if delta*delta < 0.00001 {
            return z, nil
        }
    }
}

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

//Exercise: Fibonacci closure

package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
    var r1, r2 int
    return func() int {
        r1, r2 = r2, r1+r2
        if r2 == 0{
            r2 = 1
        }
        return r1
    }
}

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

//Exercise: Slices

package main

import "code.google.com/p/go-tour/pic"

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

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

//Exercise: Loops and Functions

package main

import (
    "fmt"
)

func Sqrt(x float64) float64 {
    var z float64 = 1
    var delta float64
    for {
        delta = (z*z - x)/(2*z)
        z = z - delta
        if delta*delta < 0.00001 {
            return z
        }
    }
    
}

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

//Exercise: Maps

package main
 
import (
	"code.google.com/p/go-tour/wc"
	"strings"
)
 
func WordCount(s string) map[string]int {
	m := make(map[string]int)
	for _,w := range strings.Fields(s) {
		m[w]++
	}
	return m
}
 
func main() {
	wc.Test(WordCount)
}


//For fibonacci:

//Is it a little bit better?
func fibonacci() func() int {
  r1, r2 := 1, 0
  return func() int {
    r1, r2 = r2, r1 + r2
    return r1
  }
}