//萬年歷輸入年份月份查找當月的日歷
            #region

            Console.WriteLine("==========================Max Jiang的萬年歷=========================\n");

            int[] daysArr = new int[12] { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

            Console.Write("請輸入 1900 至 2099 年之間的年份：");
            
 
int inputYear = Convert.ToInt32(Console.ReadLine());

            Console.Write("請輸入查詢的月份：");
            int inputMonth = Convert.ToInt32(Console.ReadLine());

            int yearDays = 0;
            for (int year = 1900; year <= inputYear - 1; year++)
            {
                if ((year % 4 == 0
 
 && year % 100 != 0) || year % 400 == 0)
                {
                    yearDays += 366;
                }
                else
                {
                    yearDays += 365;
                }
            }
            //Console.WriteLine(yearDays);
            int monthDays = 0;
            Console.WriteLine(
 
"---------------------第" + inputYear + "年------------第" + inputMonth + "月份--------------------\n");
            for (int month = 0; month < inputMonth - 1; month++)
            {
                if ((inputYear % 4 == 0 && inputYear % 100 != 0) || inputYear % 400 == 0)
                {
                    daysArr[1] = 29;
                    monthDays += daysArr[month];
                }
                else
                {
                    daysArr[1] = 28;
                    monthDays += daysArr[month];
                }
            }
            //Console.Write(monthDays);
            yearDays += monthDays;  //計算出輸入的前一月的天數總和

            ////這是將知道的每月的第一天星期幾，放在相對應的周幾

            int dayOfWeek = yearDays % 7 + 1;   //通過總天數計算周數，加1為了計算下一月的第一天星期幾
            //Console.WriteLine("本月第一天是星期" + dayOfWeek);
            int[,] weeks = new int[(daysArr[inputMonth - 1] / 7) + 1, 7];//二位數組，加載周


            Console.WriteLine("星期一\t星期二\t星期三\t星期四\t星期五\t星期六\t星期日\t");
            int cols = 0;
            int m = 1;
            switch (dayOfWeek)
            {
                case 1: cols = 0; break;
                case 2: cols = 1; break;
                case 3: cols = 2; break;
                case 4: cols = 3; break;
                case 5: cols = 4; break;//通過列cols承載星期幾
                case 6: cols = 5; break;
                case 7: cols = 6; break;
                default: break;
            }
            for (int row = 0; row < (daysArr[inputMonth - 1] / 7) + 1; row++)
            {
                if (cols != 0)
                {
                    for (int i = 0; i < cols; i++)
                    {
                        weeks[row, i] = 0;//如果新月份的第一天不是星期一，用空填充星期
                        Console.Write("\t");
                    }
                }
                for (; cols < 7; cols++)//通過cols給每一列賦值，也就是天數
                {
                    if (m <= daysArr[inputMonth - 1])//小於沒月份的天數
                    {
                        weeks[row, cols] = m;
                        Console.Write("\0\0" + m + "\t");
                        ++m;
                    }
                }
                cols = 0;//循環給零，不能放上面，因為就不能循環為零
                Console.WriteLine();
            }

            #endregion

自己沒事瞎寫的，有想法請評論。

萬年歷算法