Dongle dunkey

unit1/README.md

@@ -152,11 +152,11 @@ Read more about slices in [go blog article](https://go.dev/blog/slices-intro)
 1. `numbers.append(3)`
 2. `numbers.insert(3, 3)`
 3. `append(numbers, 3)`
-4. `numbers = append(numbers, 3)`
+4. `numbers = append(numbers, 3)` - this doing it
 
 #### Q2. From where is the variable fooVar accessible if it is declared outside of any functions in a file in package fooPackage located inside module fooModule
 
-1. anywhere inside `fooPackage`, not the rest of `fooModule`
+1. anywhere inside `fooPackage`, not the rest of `fooModule` - here
 2. by any application that imports `fooModule`
 3. from anywhere in `fooModule`
 4. by other packages in `fooModule` as long as they import `fooPackage`
@@ -172,7 +172,7 @@ Read more about slices in [go blog article](https://go.dev/blog/slices-intro)
 
 1. `for i,r:=0,rand.Int(); i < r%10; i++ { ... }`
 2. `for { ... }`
-3. `{ ... } for false` 
+3. `{ ... } for false` -- here is a failure
 4. `for _,c := range "foobar" { ... }`
 
 ## Excercises

unit1/exercises/e1/main.go

@@ -0,0 +1,32 @@
+package main
+
+import "fmt"
+
+// fibonacci is a function that returns
+// a function that returns an int.
+func fibonacci() func() int {
+	x := 0
+	y := x
+	z := x
+	return func() int {
+		if z == 0 {
+			z = 1
+			return 0
+		} else if y == 0 {
+			z = z + y
+			y = 1
+		} else {
+			z = x + y
+			x = y
+			y = z
+		}
+		return z
+	}
+}
+
+func main() {
+	f := fibonacci()
+	for i := 0; i < 10; i++ {
+		fmt.Println(f())
+	}
+}

unit1/exercises/e2/main.go

@@ -0,0 +1,29 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+type IPAddr [4]byte
+
+// TODO: Add a "String() string" method to IPAddr.
+
+func (ip IPAddr) String() string {
+	var s []string
+	for _, value := range ip {
+		s = append(s, strconv.Itoa(int(value)))
+	}
+	return strings.Join(s, ".")
+}
+
+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)
+	}
+}

unit1/exercises/e3/main.go

@@ -0,0 +1,36 @@
+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) {
+	//var e ErrNegativeSqrt
+	epsilon := 0.0000000000001
+	z := x / 2
+	i := 1
+	if x < 0 {
+		return 0, ErrNegativeSqrt(x)
+	}
+	for {
+		delta := (z*z - x) / (2 * z)
+		if delta < epsilon && delta > -epsilon {
+			break
+		}
+		z -= delta
+		//fmt.Println(i," : ", z)
+		i += 1
+	}
+	return z, nil
+}
+
+func main() {
+	fmt.Println(Sqrt(2))
+	fmt.Println(Sqrt(-2))
+}

unit1/exercises/e4/main.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"io"
+	"os"
+	"strings"
+	// "fmt"
+)
+
+type rot13Reader struct {
+	r io.Reader
+}
+
+func (r rot13Reader) Read(p []byte) (n int, err error) {
+	n, err = r.r.Read(p)
+	// fmt.Printf("read %v bytes\n", n)
+	for i := range p {
+		p[i] = rot13(p[i])
+	}
+	return n, err
+}
+func rot13(b byte) byte {
+	if b >= 'A' && b <= 'Z' {
+		b = 'A' + (b-'A'+13)%26
+	} else if b >= 'a' && b <= 'z' {
+		b = 'a' + (b-'a'+13)%26
+	}
+	return b
+}
+
+func main() {
+	s := strings.NewReader("Lbh penpxrq gur pbqr!")
+	r := rot13Reader{s}
+	io.Copy(os.Stdout, &r)
+}