全部清除

本课属于 Coddy Kotlin 学习旅程的“基础知识”单元。第 89 课，共 93 课。

挑战

中等

在上一课中，你实现了“总计和平均值”功能。现在，为选项 4 实现“全部清除”功能。

修改程序以处理选项 4：

从 expenses 列表中清除所有费用
输出 All expenses cleared!

其他选项应继续像以前一样正常工作：

选项 1：添加费用
选项 2：查看所有费用
选项 3：总计和平均值
选项 5：输出 Goodbye! 并退出
无效选项：输出 Invalid option

输入格式：

菜单选项和费用金额均为字符串。

输出格式：

先显示菜单，然后根据每项操作给出相应的响应。

示例：

如果输入依次为 1、50.0、1、25.0、2、4、2 和 5，输出应为：

--- Expense Tracker ---
1. Add Expense
2. View All Expenses
3. Total and Average
4. Clear All
5. Exit
Choose an option:
Enter expense amount:
Expense added!
--- Expense Tracker ---
1. Add Expense
2. View All Expenses
3. Total and Average
4. Clear All
5. Exit
Choose an option:
Enter expense amount:
Expense added!
--- Expense Tracker ---
1. Add Expense
2. View All Expenses
3. Total and Average
4. Clear All
5. Exit
Choose an option:
Your expenses:
- $50.0
- $25.0
--- Expense Tracker ---
1. Add Expense
2. View All Expenses
3. Total and Average
4. Clear All
5. Exit
Choose an option:
All expenses cleared!
--- Expense Tracker ---
1. Add Expense
2. View All Expenses
3. Total and Average
4. Clear All
5. Exit
Choose an option:
No expenses recorded.
--- Expense Tracker ---
1. Add Expense
2. View All Expenses
3. Total and Average
4. Clear All
5. Exit
Choose an option:
Goodbye!

提示：对可变列表使用 clear() 方法可以移除所有元素。

亲手试试

fun main() {
    val expenses = mutableListOf<Double>()
    
    while (true) {
        println("--- Expense Tracker ---")
        println("1. Add Expense")
        println("2. View All Expenses")
        println("3. Total and Average")
        println("4. Clear All")
        println("5. Exit")
        println("Choose an option:")
        
        val choice = readLine()
        
        if (choice == "1") {
            println("Enter expense amount:")
            val amount = readLine()!!.toDouble()
            expenses.add(amount)
            println("Expense added!")
        } else if (choice == "2") {
            if (expenses.isEmpty()) {
                println("No expenses recorded.")
            } else {
                println("Your expenses:")
                for (expense in expenses) {
                    println("- \$$expense")
                }
            }
        } else if (choice == "3") {
            if (expenses.isEmpty()) {
                println("No expenses recorded.")
            } else {
                val total = expenses.sum()
                val average = total / expenses.size
                println("Total: \$$total")
                println("Average: \$$average")
            }
        } else if (choice == "5") {
            println("Goodbye!")
            break
        } else {
            println("Invalid option")
        }
    }
}

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