Strings (Text) — Programuoki

Code

Refactor main.go — a clean display and a real check

The menu loop stays exactly as it was — we add two functions and one check. Everything else in your main.go is untouched.

1. A correct title check — validateTitle. It counts characters (runes), not bytes:

func validateTitle(title string) string {
	title = strings.TrimSpace(title)
	n := utf8.RuneCountInString(title)
	if n == 0 {
		return "Title cannot be empty."
	}
	if n > 60 {
		return fmt.Sprintf("Title is too long: %d characters (max 60).", n)
	}
	return ""
}

Had we written len(title) > 60, a Lithuanian title with diacritics would be rejected too early — len counts bytes. This one function is step 2's gotcha, applied. (Add "unicode/utf8" to the imports.)

2. Use it in "Set title". One check added inside case "2" — validate before storing:

		case "2":
			fmt.Print("New title: ")
			title := readLine()
			if msg := validateTitle(title); msg != "" {
				fmt.Println(msg)
				continue
			}
			it.Title = title
			fmt.Println("Title set to:", title)

3. A clean, ALIGNED display — formatItem. %-30s left-aligns the title in a 30-column field, %3d/%-3d pads the numbers, so rows line up:

func formatItem(it Item) string {
	status := "reading"
	if it.Read {
		status = "done"
	}
	return fmt.Sprintf("%-30s %3d/%-3d  [%s]", it.Title, it.PagesRead, it.Pages, status)
}

printItem now just calls it — fmt.Println(formatItem(it)). In lesson 8, with many records, the alignment pays off: a tidy table for free.

Verify — set a multi-word Lithuanian title, then show it:

> 2
New title: Ąžuolas ir uosis
Title set to: Ąžuolas ir uosis

> 1
Ąžuolas ir uosis                 0/380  [reading]

The title is read in full (spaces included — readLine from lesson 5), and the columns line up.

Gotcha (fmt.Scanln and spaces). If you read the title with fmt.Scanln(&title), "Ąžuolas ir uosis" becomes just "Ąžuolas" — the rest of the line stays in the buffer and scrambles the next read. For multi-word text, always read the whole line with readLine, not Scanln.

main.go MODIFY 26 lines changed

Edit this file in ./

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
	"unicode/utf8"
)

const appName = "Book list"

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

// scanner is the ONE place the program reads keyboard input.
var scanner = bufio.NewScanner(os.Stdin)

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

	for {
		fmt.Println("\n1) Show  2) Set title  3) Set pages  4) Mark read  5) Pages read  6) Progress  q) Quit")
		fmt.Print("> ")

		switch readLine() {
		case "1":
			printItem(it)
		case "2":
			fmt.Print("New title: ")
			title := readLine()
			if msg := validateTitle(title); msg != "" {
				fmt.Println(msg)
				continue
			}
			it.Title = title
			fmt.Println("Title set to:", title)
		case "3":
			it.Pages = readInt("Pages: ") // retries until a whole number
			fmt.Println("Pages set to:", it.Pages)
		case "4":
			it.Read = true
			fmt.Println("Marked as read.")
		case "5":
			// readInt (from lesson 5) guarantees a whole number; we still
			// check the BOUNDS ourselves — 0..Pages.
			n := readInt("Pages read: ")
			if n < 0 || n > it.Pages {
				fmt.Println("Out of range (0 ..", it.Pages, ").")
				continue
			}
			it.PagesRead = n
			fmt.Println("Saved:", n, "pages.")
		case "6":
			fmt.Printf("Progress: %.1f%%\n", progressPercent(it))
		case "q":
			fmt.Println("Bye!")
			return
		default:
			fmt.Println("Unknown choice — try again.")
		}
	}
}

// validateTitle checks the title's REAL length in characters (runes), not bytes.
// len("ąžuolas") is 9 (bytes) but utf8.RuneCountInString is 7 (characters) — a
// Lithuanian title must not be rejected for the wrong length.
func validateTitle(title string) string {
	title = strings.TrimSpace(title)
	n := utf8.RuneCountInString(title)
	if n == 0 {
		return "Title cannot be empty."
	}
	if n > 60 {
		return fmt.Sprintf("Title is too long: %d characters (max 60).", n)
	}
	return ""
}

// 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
}

// readLine reads ONE whole line of input (spaces included) and trims it.
// Unlike fmt.Scanln, which stops at the first space, this reads a full title
// like "Buy milk" instead of just "Buy".
func readLine() string {
	scanner.Scan()
	return strings.TrimSpace(scanner.Text())
}

// readInt keeps asking until the user types a whole number — the retry loop.
func readInt(prompt string) int {
	for {
		fmt.Print(prompt)
		n, err := strconv.Atoi(readLine())
		if err == nil {
			return n
		}
		fmt.Println("Please enter a whole number.")
	}
}

// printHeader prints the app title line (from lesson 3).
func printHeader() {
	fmt.Println("App:", appName)
}

// formatItem builds a clean, ALIGNED one-line summary. %-30s left-aligns the
// title in a 30-column field so a list of items lines up.
func formatItem(it Item) string {
	status := "reading"
	if it.Read {
		status = "done"
	}
	return fmt.Sprintf("%-30s %3d/%-3d  [%s]", it.Title, it.PagesRead, it.Pages, status)
}

func printItem(it Item) {
	fmt.Println(formatItem(it))
}