using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("原本的 List:");

        var origin = new List<Person> {

            new Person { Name = "p1", Age = 10 },

            new Person { Name = "p2", Age = 20 },

            new Person { Name = "p3", Age = 30 },

            new Person { Name = "p4", Age = 40 },

            new Person { Name = "p5", Age = 50 }

        };

        PrintList(origin);

        // ------------------------ Start -----------------------

        // 我想透過判斷 Age > 30 來刪掉符合條件的 Person

        var count = origin.Count;

        /*

        // 不論你是用 foreach 或是正著刪除都會 run-time 引發問題

        for(var i = 0; i < count; i++)

        {

            if( origin[i].Age > 30)

            {

                origin.RemoveAt(i);

            }

        }

        Run-time exception (line 28): Index was out of range. Must be non-negative and less than the size of the collection.

        Parameter name: index

        Stack Trace:

        [System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.

        Parameter name: index]

          at Program.Main(): line 28

        */

        // 倒著刪除

        // 就不會發生 Index 溢位的問題囉 ~

        /*

        for(var i = count - 1; i >= 0; i--)

        {

            if( origin[i].Age > 30)

            {

                origin.RemoveAt(i);

            }

        }

        */

        // 直接使用 RemoveAll

        origin.RemoveAll(r => r.Age> 30);

        // ------------------------ End -----------------------

        Console.WriteLine("刪除過後的 List:");

        PrintList(origin);

    }

    public static void PrintList(List<Person> PList) 

    {

        foreach(var p in PList)

        {

            Console.WriteLine(p.Name);

        }

    }

    public class Person

    {

        public string Name;

        public int Age;

    }

}