《go语言程序设计》学习（五）

package main
import (
    "bufio"
    "fmt"
    "math"
    "os"
)
const result = "Polar radius=%.02f θ=%.02f° → 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."
type polar struct {
    radius float64
    tt     float64
}
type cartesian struct {
    x float64
    y float64
}
func init() {
    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
            tt := polarCoord.tt * math.Pi / 180
            x := polarCoord.radius * math.Cos(tt)
            y := polarCoord.radius * math.Sin(tt)
            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
        }
        var radius, tt float64
        if _, err := fmt.Sscanf(line, "%f %f", &radius, &tt); err != nil {
            fmt.Println(os.Stderr, "invalid input")
            continue
        }
        questions <- polar{radius, tt}
        coord := <-answers
        fmt.Printf(result, radius, tt, coord.x, coord.y)
    }
    fmt.Println()
}