处理无效输入

本课属于 Coddy Lua 学习旅程的“逻辑与流程”单元。第 47 课，共 54 课。

挑战

简单

通过妥善处理无效的菜单命令，完成你的联系人列表应用。当用户输入的命令与任何可用选项都不匹配时，程序应告知用户，并继续运行。

在上一个挑战的基础上，添加一个 else 条件，用来处理不是 add、list、search、delete 或 quit 的命令。这样，当用户输入无法识别的命令时，程序就能给出明确的反馈，提升用户体验。

要求：

保留上一个挑战中的所有代码，包括设置、显示菜单、主循环，以及添加、列出、搜索和删除功能
添加一个 else 条件，用来处理与有效选项都不匹配的命令
输入无效命令时，打印：Invalid command. Please try again.
显示无效命令消息后，程序应继续运行
所有现有命令（add、list、search、delete、quit）仍应像之前一样正常工作

交互示例：

Welcome to Contact List Manager!

Available Commands:
add - Add a new contact
list - Display all contacts
search - Search for a contact
delete - Delete a contact
quit - Exit the program

Enter command:
add
Enter name:
Alice
Enter phone number:
555-1234
Contact added successfully!

Enter command:
show
Invalid command. Please try again.

Enter command:
remove
Invalid command. Please try again.

Enter command:
list
Contact List:
1. Alice - 555-1234

Enter command:
help
Invalid command. Please try again.

Enter command:
quit
Goodbye!

亲手试试

-- Contact List Manager with Delete Functionality
local contacts = {}

print("Welcome to Contact List Manager!")
print()
print("Available Commands:")
print("add - Add a new contact")
print("list - Display all contacts")
print("search - Search for a contact")
print("delete - Delete a contact")
print("quit - Exit the program")
print()

while true do
    print("Enter command:")
    local command = io.read()
    
    if command == "add" then
        print("Enter name:")
        local name = io.read()
        print("Enter phone number:")
        local phone = io.read()
        
        local contact = {name = name, phone = phone}
        table.insert(contacts, contact)
        print("Contact added successfully!")
        print()
        
    elseif command == "list" then
        if #contacts == 0 then
            print("No contacts available.")
        else
            print("Contact List:")
            for i, contact in ipairs(contacts) do
                print(i .. ". " .. contact.name .. " - " .. contact.phone)
            end
        end
        print()
        
    elseif command == "search" then
        print("Enter name to search:")
        local searchName = io.read()
        local found = false
        
        for i, contact in ipairs(contacts) do
            if contact.name == searchName then
                print("Found: " .. contact.name .. " - " .. contact.phone)
                found = true
                break
            end
        end
        
        if not found then
            print("Contact not found.")
        end
        print()
        
    elseif command == "delete" then
        print("Enter name to delete:")
        local deleteName = io.read()
        local found = false
        
        for i, contact in ipairs(contacts) do
            if contact.name == deleteName then
                table.remove(contacts, i)
                print("Contact deleted successfully!")
                found = true
                break
            end
        end
        
        if not found then
            print("Contact not found.")
        end
        print()
        
    elseif command == "quit" then
        print("Goodbye!")
        break
    end
end