Go 언어에서 std-in

// bill.go
package main

import (
	"fmt"
)

type bill struct {
	name  string
	items map[string]float64
	tip   float64
}

// format the bill
func (b bill) format() string {
	fs := "Bill breakdown: \n"
	var total float64 = 0

	// list items
	for k, v := range b.items {
		fs += fmt.Sprintf("%-25v ...$%v \n", k+":", v)
		total += v
	}

	// add tip
	fs += fmt.Sprintf("%-25v ...$%v \n", "tip:", b.tip)

	// total
	fs += fmt.Sprintf("%-25v ...$%0.2f", "total:", total+b.tip)

	return fs
}

// make new bills
func newBill(name string) bill {
	b := bill{
		name:  name,
		items: map[string]float64{},
		tip:   0,
	}
	return b
}

// update tip
func (b *bill) updateTip(tip float64) {
	b.tip = tip
}

// add an item to the bill
func (b *bill) addItem(name string, price float64) {
	b.items[name] = price
}

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

// Helper function
func getInput(prompt string, r *bufio.Reader) (string, error) {
	fmt.Print(prompt)
	input, err := r.ReadString('\n')

	return strings.TrimSpace(input), err
}

func createBill() bill {
	reader := bufio.NewReader(os.Stdin)
	name, _ := getInput("Create a new bill name: ", reader)
	b := newBill(name)
	fmt.Println("Created the bill - ", b.name)

	return b
}

// save bill
func (b bill) save() {
	data := []byte(b.format())

	err := os.WriteFile(b.name+".txt", data, 0644)
	if err != nil {
		panic(err)
	}
	fmt.Println("bill was saved to file.")
}

func promptOptions(b bill) {
	reader := bufio.NewReader(os.Stdin)
	opt, _ := getInput("Choose option (a - add item, s - save bill, t - add tip)", reader)
	switch opt {
	case "a":
		name, _ := getInput("Item name: ", reader)
		price, _ := getInput("Item price: ", reader)

		p, err := strconv.ParseFloat(price, 64)
		if err != nil {
			fmt.Println("The price must be a number")
			promptOptions(b)
		}

		b.addItem(name, p)
		fmt.Println("item added - ", name, price)
		promptOptions(b)
	case "t":
		tip, _ := getInput("Enter tip amount ($):", reader)

		t, err := strconv.ParseFloat(tip, 64)
		if err != nil {
			fmt.Println("The tip must be a number")
			promptOptions(b)
		}

		b.updateTip(t)
		fmt.Println("tip added - ", tip)
		promptOptions(b)
	case "s":
		b.save()
		fmt.Println("you save the file - ", b.name+".txt")
	default:
		fmt.Println("that was not a valid option...")
		promptOptions(b)
	}
}

func main() {
	mybill := createBill()
	promptOptions(mybill)

}

// 결과
//
// Create a new bill name: luigi
// Created the bill -  luigi
// Choose option (a - add item, s - save bill, t - add tip)a
// Item name: veg stew
// Item price: 6.99
// item added -  veg stew 6.99
// Choose option (a - add item, s - save bill, t - add tip)a
// Item name: toffee pudding
// Item price: 5.25
// item added -  toffee pudding 5.25
// Choose option (a - add item, s - save bill, t - add tip)t
// Enter tip amount ($):7
// tip added -  7
// Choose option (a - add item, s - save bill, t - add tip)s
// bill was saved to file.
// you save the file -  luigi.txt