C#でコンソール画面でのカレンダー作ってみた

Test.cs

using System.Collections.Generic;
using static System.Linq.Enumerable;
using static System.Console;
class Sub : object
{
    const int WEEK_MAX = 7;//マジックナンバーは禁止

    public Sub()
    {
    }

    public int Week()
    {
        WriteLine("1/1の曜日を入力");
        switch (ReadLine())
        {
            case "日":
            case "日曜日":
                return 1;
            case "月":
            case "月曜日":
                return 2;
            case "火":
            case "火曜日":
                return 3;
            case "水":
            case "水曜日":
                return 4;
            case "木":
            case "木曜日":
                return 5;
            case "金":
            case "金曜日":
                return 6;
            case "土":
            case "土曜日":
                return 7;
            default:
                return 0;
        }
    }

    public string Calendar(int year,int you)
    {
        if (year <= 0 || you == 0)
        {
            return null;
        }
        WriteLine($"{year}年カレンダー\n");
        var cld = "";
        int max;
        foreach (var y in Range(1, 12))
        {
            cld += $"{y.ToString()}月のカレンダー\n\n"; 
            if (y == 4 || y == 6 || y == 9 || y == 11)
            {
                max = 30;
            }
            else if (y == 2)
            {
                if (year % 4 == 0 && !(year % 100 == 0 && year % 400 != 0))
                {
                    max = 29;
                }
                else
                {
                    max = 28;
                }
            }
            else
            {
                max = 31;
            }
            cld += "日月火水木金土\n";
            foreach (var x in Range(1, max))
            {
                if (x < 10)
                {
                    cld += " ";
                }
                if (x == 1)
                {
                    if (you == 0)
                    {
                        you += 1;
                    }
                    foreach(var z in Range(1, you-1))
                    {
                        cld += "  ";
                    }
                }
                if (you % WEEK_MAX == 0)
                {
                    you %= WEEK_MAX;
                    cld += x.ToString() + "\n";
                }
                else
                {
                    cld += x.ToString();
                }
                you++;
            }
            cld += "\n\n";
        }
        return cld;
    }

    public void End()
    {
        WriteLine("何かを入力してください");
        ReadLine().ToString();
    }

}

class Test
{
    static void Main(string[] args)
    {
        var sub = new Sub();
        Write("調べたい年を入力");
        var year = int.Parse(ReadLine());
        var cld = sub.Calendar(year,sub.Week());
        WriteLine(cld is null? "\n存在しないです\n":cld);
        sub.End();
    }
}