update book code

eBook/exercises/chapter_14/polar_to_cartesian.go

@@ -0,0 +1,101 @@
+// polartocartesian.go
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"math"
+	"os"
+	"runtime"
+	"strconv"
+	"strings"
+)
+
+type polar struct {
+	radius float64
+	Θ      float64
+}
+
+type cartesian struct {
+	x float64
+	y float64
+}
+
+const result = "Polar: radius=%.02f angle=%.02f degrees -- Cartesian: x=%.02f y=%.02f\n"
+
+var prompt = "Enter a radius and an angle (in degrees), e.g., 12.5 90, " + "or %s to quit."
+
+func init() {
+	if runtime.GOOS == "windows" {
+		prompt = fmt.Sprintf(prompt, "Ctrl+Z, Enter")
+	} else { // Unix-like
+		prompt = fmt.Sprintf(prompt, "Ctrl+D")
+	}
+}
+
+func main() {
+	questions := make(chan polar)
+	defer close(questions)
+	answers := createSolver(questions)
+	defer close(answers)
+	interact(questions, answers)
+}
+
+func createSolver(questions chan polar) chan cartesian {
+	answers := make(chan cartesian)
+	go func() {
+		for {
+			polarCoord := <-questions
+			Θ := polarCoord.Θ * math.Pi / 180.0 // degrees to radians
+			x := polarCoord.radius * math.Cos(Θ)
+			y := polarCoord.radius * math.Sin(Θ)
+			answers <- cartesian{x, y}
+		}
+	}()
+	return answers
+}
+
+func interact(questions chan polar, answers chan cartesian) {
+	reader := bufio.NewReader(os.Stdin)
+	fmt.Println(prompt)
+	for {
+		fmt.Printf("Radius and angle: ")
+		line, err := reader.ReadString('\n')
+		if err != nil {
+			break
+		}
+		line = line[:len(line)-1] // chop of newline character
+		if numbers := strings.Fields(line); len(numbers) == 2 {
+			polars, err := floatsForStrings(numbers)
+			if err != nil {
+				fmt.Fprintln(os.Stderr, "invalid number")
+				continue
+			}
+			questions <- polar{polars[0], polars[1]}
+			coord := <-answers
+			fmt.Printf(result, polars[0], polars[1], coord.x, coord.y)
+		} else {
+			fmt.Fprintln(os.Stderr, "invalid input")
+		}
+	}
+	fmt.Println()
+}
+
+func floatsForStrings(numbers []string) ([]float64, error) {
+	var floats []float64
+	for _, number := range numbers {
+		if x, err := strconv.ParseFloat(number, 64); err != nil {
+			return nil, err
+		} else {
+			floats = append(floats, x)
+		}
+	}
+	return floats, nil
+}
+/* Output:
+Enter a radius and an angle (in degrees), e.g., 12.5 90, or Ctrl+Z, Enter to qui
+t.
+Radius and angle: 12.5 90
+Polar: radius=12.50 angle=90.00 degrees -- Cartesian: x=0.00 y=12.50
+Radius and angle: ^Z
+*/