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Pertvarkyk main.go — skaitinis laukas su patikra

Sujungiam abu žingsnius į programą — meniu gauna du naujus punktus.

Kas naujo, lyginant su 5 pamokos versija:

Item gavo lauką PagesRead int (perskaityti puslapiai).
3) Set pages read — pilnas 1 žingsnio šablonas: Scanln → Atoi → patikra (err != nil || n < 0 || n > it.Pages) → arba išsaugom, arba mandagiai atsisakom.
4) Progress — progressPercent funkcija su teisinga float64 dalyba ir apsauga nuo dalybos iš nulio.
formatItem dabar rodo 190/380 formą.

Patikrink — suvesk 4, 3 + 190, 4, 3 + abc, 1, q:

> 4
Progress: 0.0%
> 3
Pages read: 190
Saved: 190 pages.
> 4
Progress: 50.0%
> 3
Pages read: abc
Not a valid number of pages.
> 1
Book: The Go Programming Language | pages: 190/380 | read: false
> q
Bye!

Esmė matosi antrame 4: 50.0%, ne 0% — dalyba vyksta float64 pasaulyje.

Patarimas. Pakeisk progressPercent viduje float64(it.PagesRead) / float64(it.Pages) į it.PagesRead / it.Pages ir paleisk dar kartą — pamatyk 0% savo akimis. Sugadinti ir pataisyti — geriausias būdas įsiminti.

main.go MODIFIKUOTI

Redaguok šį failą kataloge ./

package main

import (
	"fmt"
	"strconv"
)

const appName = "Book list"

// Item is one record of the list.
type Item struct {
	Title     string
	Pages     int
	PagesRead int
	Read      bool
}

func main() {
	it := Item{Title: "The Go Programming Language", Pages: 380}

	fmt.Println("App:", appName)

	for {
		fmt.Println("\n1) Show item  2) Mark read  3) Set pages read  4) Progress  q) Quit")
		fmt.Print("> ")

		var choice string
		fmt.Scanln(&choice)

		switch choice {
		case "1":
			printItem(it)
		case "2":
			it.Read = true
			fmt.Println("Marked as read.")
		case "3":
			fmt.Print("Pages read: ")
			var raw string
			fmt.Scanln(&raw)
			n, err := strconv.Atoi(raw)
			if err != nil || n < 0 || n > it.Pages {
				fmt.Println("Not a valid number of pages.")
				continue
			}
			it.PagesRead = n
			fmt.Println("Saved:", n, "pages.")
		case "4":
			fmt.Printf("Progress: %.1f%%\n", progressPercent(it))
		case "q":
			fmt.Println("Bye!")
			return
		default:
			fmt.Println("Unknown choice — try again.")
		}
	}
}

// progressPercent returns how much of the book is read, in percent.
// Both sides are converted to float64 BEFORE dividing — integer division
// would silently truncate 190/380 to 0.
func progressPercent(it Item) float64 {
	if it.Pages == 0 {
		return 0
	}
	return float64(it.PagesRead) / float64(it.Pages) * 100
}

// formatItem builds the one-line summary for a single record.
func formatItem(it Item) string {
	return fmt.Sprintf("Book: %s | pages: %d/%d | read: %v", it.Title, it.PagesRead, it.Pages, it.Read)
}

// printItem prints the summary built by formatItem.
func printItem(it Item) {
	fmt.Println(formatItem(it))
}