more exercises

exercise-errors.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+    "fmt"
+    "math"
+)
+
+type ErrNegativeSqrt float64
+
+func (e ErrNegativeSqrt) Error() string {
+    return fmt.Sprintf("cannot Sqrt negative number: %f", float64(e))
+}
+
+func Sqrt(x float64) (float64, error) {
+    if x < 0 {
+        return 0, ErrNegativeSqrt(x)
+    }
+    var p float64
+    for z := 1.0; z != p && math.Abs(z - p) > 0.000000000000001; z -= (z * z - x) / (2 * z) {
+        p = z
+    }
+    return p, nil
+}
+
+func main() {
+    fmt.Println(Sqrt(4))
+    fmt.Println(Sqrt(-2))
+}

exercise-reader.go

@@ -0,0 +1,19 @@
+package main
+
+import "golang.org/x/tour/reader"
+
+type MyReader struct{}
+
+// TODO: Add a Read([]byte) (int, error) method to MyReader.
+
+func (MyReader) Read(b []byte) (int, error) {
+    c := "A"
+    for i := range b {
+        b[i] = byte(c[0])
+    }
+    return len(b), nil
+}
+
+func main() {
+	reader.Validate(MyReader{})
+}

exercise-rot-reader.go

@@ -0,0 +1,42 @@
+package main
+
+import (
+    "io"
+    "os"
+    "strings"
+)
+
+type rot13Reader struct {
+    r io.Reader
+}
+
+var rot13Input  []byte = []byte("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz")
+var rot13Output []byte = []byte("NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm")
+
+func indexOf(s []byte, b byte) int {
+    for i, v := range s {
+        if v == b {
+            return i
+        }
+    }
+    return -1
+}
+
+func (r rot13Reader) Read(b []byte) (n int, err error) {
+    n, err = r.r.Read(b)
+    if err == nil {
+        for i := 0; i < n; i++ {
+            c := b[i]
+            if j := indexOf(rot13Input, c); j > -1 {
+                b[i] = rot13Output[j]
+            }
+        }
+    }
+    return n, err
+}
+
+func main() {
+    s := strings.NewReader("Lbh penpxrq gur pbqr!")
+    r := rot13Reader{s}
+    io.Copy(os.Stdout, &r)
+}

reader.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+    "fmt"
+    "io"
+    "strings"
+)
+
+func main() {
+    r := strings.NewReader("Hello, Reader!")
+
+    b := make([]byte, 8)
+    for {
+        n, err := r.Read(b)
+        fmt.Printf("n = %v err = %v b = %v\n", n, err, b)
+        fmt.Printf("b[:n] = %q\n", b[:n])
+        if err == io.EOF {
+            break
+        }
+    }
+}