update book code

eBook/exercises/chapter_13/Makefile

@@ -0,0 +1,6 @@
+include $(GOROOT)/src/Make.inc
+TARG=strev
+GOFILES=\
+	string_reverse.go\
+
+include $(GOROOT)/src/Make.pkg

eBook/exercises/chapter_13/panic_defer.go

@@ -0,0 +1,44 @@
+// panic_defer.go
+package main
+
+import "fmt"
+
+func main() {
+	f()
+	fmt.Println("Returned normally from f.")
+}
+
+func f() {
+	defer func() {
+		if r := recover(); r != nil {
+			fmt.Println("Recovered in f", r)
+		}
+	}() 
+	fmt.Println("Calling g.")
+	g(0)
+	fmt.Println("Returned normally from g.")
+}
+
+func g(i int) {
+	if i > 3 {
+		fmt.Println("Panicking!")
+		panic(fmt.Sprintf("%v", i))
+	}
+	defer fmt.Println("Defer in g", i)
+	fmt.Println("Printing in g", i)
+	g(i + 1)
+}
+/* Output:
+Calling g.
+Printing in g 0
+Printing in g 1
+Printing in g 2
+Printing in g 3
+Panicking!
+Defer in g 3
+Defer in g 2
+Defer in g 1
+Defer in g 0
+Recovered in f 4
+Returned normally from f.
+*/

eBook/exercises/chapter_13/panic_defer_convint.go

@@ -0,0 +1,44 @@
+// panic_defer_convint.go
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+func main() {
+	l := int64(15000)
+	if i, err := IntFromInt64(l); err!= nil {
+		fmt.Printf("The conversion of %d to an int32 resulted in an error: %s", l, err.Error())
+	} else {
+		fmt.Printf("%d converted to an int32 is %d", l, i)
+	}
+	fmt.Println()
+	l = int64(math.MaxInt32 + 15000)
+	if i, err := IntFromInt64(l); err!= nil {
+		fmt.Printf("The conversion of %d to an int32 resulted in an error: %s", l, err.Error())
+	} else {
+		fmt.Printf("%d converted to an int32 is %d", l, i)
+	}
+}
+
+func ConvertInt64ToInt(l int64) int {
+    if math.MinInt32 <= l && l <= math.MaxInt32 {
+        return int(l)
+    }
+    panic(fmt.Sprintf("%d is out of the int32 range", l))
+}
+
+func IntFromInt64(l int64) (i int, err error) {
+    defer func() {
+        if e := recover(); e != nil {
+            err = fmt.Errorf("%v", e)
+        }
+    }()
+    i = ConvertInt64ToInt(l)
+    return i, nil
+}
+/* Output:
+15000 converted to an int32 is 15000
+The conversion of 2147498647 to an int32 resulted in an error: 2147498647 is out of the int32 range
+*/

eBook/exercises/chapter_13/recover_divbyzero.go

@@ -0,0 +1,34 @@
+// recover_divbyzero.go
+package main
+
+import (
+	"fmt"
+)
+
+func badCall() {
+  a, b := 10, 0
+  n := a / b
+  fmt.Println(n)
+}
+
+func test() {
+   defer func() { 
+    if e := recover(); e != nil {
+       fmt.Printf("Panicing %s\r\n", e);
+    }
+   
+    }()
+    badCall()
+    fmt.Printf("After bad call\r\n");
+}
+
+func main() {
+   fmt.Printf("Calling test\r\n");
+   test()
+   fmt.Printf("Test completed\r\n");
+}
+/* Output:
+Calling test
+Panicing runtime error: integer divide by zero
+Test completed
+*/

eBook/exercises/chapter_13/string_reverse.go

@@ -0,0 +1,18 @@
+// string_reverse.go
+package strev
+
+func Reverse(s string) string {
+	runes := []rune(s)
+	n, h := len(runes), len(runes)/2
+	for i := 0; i < h; i++ {
+		runes[i], runes[n-1-i] = runes[n-1-i], runes[i]
+	}
+	return string(runes)
+}
+
+/*
+func main() {
+	s := "My Test String!"
+	fmt.Println(s, " --> ", Reverse(s))
+}
+*/

eBook/exercises/chapter_13/string_reverse_test.go

@@ -0,0 +1,40 @@
+// string_reverse_test.go
+package strev
+
+import "testing"
+import "./strev"
+
+type ReverseTest struct {
+	in, out 	string
+}
+
+var ReverseTests = []ReverseTest {
+	ReverseTest{"ABCD", "DCBA"},
+	ReverseTest{"CVO-AZ", "ZA-OVC"},
+	ReverseTest{"Hello 世界", "界世 olleH"},
+}
+
+func TestReverse(t *testing.T) {
+/*
+	in := "CVO-AZ"
+	out := Reverse(in)
+	exp := "ZA-OVC"
+	if out != exp {
+		t.Errorf("Reverse of %s expects %s, but got %s", in, exp, out)
+	}
+*/
+// testing with a battery of testdata:
+	for _, r := range ReverseTests {
+		exp := strev.Reverse(r.in)
+		if r.out != exp {
+			t.Errorf("Reverse of %s expects %s, but got %s", r.in, exp, r.out)
+		}
+	}
+}
+
+func BenchmarkReverse(b *testing.B) {
+	s := "ABCD"
+	for i:=0; i < b.N; i++ {
+		strev.Reverse(s)
+	}
+}