年月日判断并输出第多少天

 方法一：
 while (true)
            {
                Console.Write("输入年：");
                int year = int.Parse(Console.ReadLine());
                Console.Write("输入月：");
                int month = int.Parse(Console.ReadLine());
                Console.Write("输入日：");
                int day = int.Parse(Console.ReadLine());


                bool isok = false;//用来记录日期是否正确
                bool isrun = false;

                if (year >= 1759 && year < 9999)
                {
                    if (month >= 1 && month <= 12)
                    {
                        if (month == 2)
                        {
                            if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0))
                            {
                                if (day >= 1 && day <= 29)
                                {
                                    isok = true;
                                    isrun = true;
                                }
                                else
                                {
                                    Console.WriteLine("应在29天范围之内");
                                }
                            }
                            else
                            {
                                if (day >= 1 && day <= 28)
                                {
                                    isok = true;
                                }
                                else
                                {
                                    Console.WriteLine("应在28天范围之内");
                                }
                            }
                        }
                        if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12)
                        {
                            if (day >= 1 && day <= 31)
                            {
                                isok = true;
                            }
                            else
                            {
                                Console.WriteLine("日期应在31天之内");
                            }
                        }

                        if (month == 4 || month == 6 || month == 9 || month == 11)
                        {
                            if (day >= 1 && day <= 30)
                            {
                                isok = true;
                            }
                            else
                            {
                                Console.WriteLine("日期应在30天之内");
                            }
                        }
                    }
                    else
                    {
                        Console.WriteLine("月份不正确");
                    }
                }
                else
                {
                    Console.WriteLine("年份不正确");
                }


                int sumday = 0;//第多少天
                if (isok)//日期正确，计算天数
                {
                    if (isrun)//是闰年
                    {
                        if (month == 1)
                        {
                            sumday = day;
                        }
                        if (month == 2)
                        {
                            sumday = 31 + day;
                        }
                        if (month == 3)
                        {
                            sumday = 31 + 29 + day;
                        }
                        if (month == 4)
                        {
                            sumday = 31 + 29 + 31 + day;
                        }
                        if (month == 5)
                        {
                            sumday = 31 + 29 + 31 + 30 + day;
                        }
                        if (month == 6)
                        {
                            sumday = 31 + 29 + 31 + 30 + 31 + day;
                        }
                        if (month == 7)
                        {
                            sumday = 31 + 29 + 31 + 30 + 31 + 30 + day;
                        }
                        if (month == 8)
                        {
                            sumday = 31 + 29 + 31 + 30 + 31 + 30 + 31 + day;
                        }
                        if (month == 9)
                        {
                            sumday = 31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + day;
                        }
                        if (month == 10)
                        {
                            sumday = 31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + day;
                        }
                        if (month == 11)
                        {
                            sumday = 31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + day;
                        }
                        if (month == 12)
                        {
                            sumday = 31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + day;
                        }
                    }
                    else
                    {
                        if (month == 1)
                        {
                            sumday = day;
                        }
                        if (month == 2)
                        {
                            sumday = 31 + day;
                        }
                        if (month == 3)
                        {
                            sumday = 31 + 28 + day;
                        }
                        if (month == 4)
                        {
                            sumday = 31 + 28 + 31 + day;
                        }
                        if (month == 5)
                        {
                            sumday = 31 + 28 + 31 + 30 + day;
                        }
                        if (month == 6)
                        {
                            sumday = 31 + 28 + 31 + 30 + 31 + day;
                        }
                        if (month == 7)
                        {
                            sumday = 31 + 28 + 31 + 30 + 31 + 30 + day;
                        }
                        if (month == 8)
                        {
                            sumday = 31 + 28 + 31 + 30 + 31 + 30 + 31 + day;
                        }
                        if (month == 9)
                        {
                            sumday = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + day;
                        }
                        if (month == 10)
                        {
                            sumday = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + day;
                        }
                        if (month == 11)
                        {
                            sumday = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + day;
                        }
                        if (month == 12)
                        {
                            sumday = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + day;
                        }
                    }


                    Console.WriteLine("第{0}天", sumday);

                }
                else
                {
                    Console.WriteLine("已经日期不正确，算不出来！");
                }
                
                Console.ReadLine();
            }
        }
方法二：

while (true) //输入年月日判断是该年的第几天
{
int year, mooth, day;
Console.Write("请输入年份：");
year=int.Parse( Console.ReadLine());
if ((year > 1759 && year <= 9999) && (year % 400 == 0 || (year % 100 != 0 && year % 4 == 0)))
{
Console.Write("请输入月份;");
mooth = int.Parse(Console.ReadLine());
if (mooth >= 1 && mooth <= 12)
{
Console.Write("请输入日期：");
day = int.Parse(Console.ReadLine());
int m1=31, m2=28,m3=31, m4=30, m5=31, m6=30, m7=31, m8=31, m9=30, m10=31, m11=30;
if(mooth==1&&(day>=1&&day<=31))
{
Console.WriteLine("这是"+year+"第"+day+"天");
}
else if (mooth == 2 && (day >= 1 && day <= 28))
{
Console.WriteLine("这是" + year + "第" +(m1+day) + "天");
}
else if (mooth == 3 && (day >= 1 && day <= 31))
{
Console.WriteLine("这是" + year + "第" + (m1+m2+ day) + "天");
}
else if (mooth == 4 && (day >= 1 && day <= 30))
{
Console.WriteLine("这是" + year + "第" + (m1+m2+m3+ day) + "天");
}
else if (mooth == 5 && (day >= 1 && day <= 31))
{
Console.WriteLine("这是" + year + "第" + (m1+m2+m3+m4 + day) + "天");
}
else if (mooth == 6 && (day >= 1 && day <= 30))
{
Console.WriteLine("这是" + year + "第" + (m1+m2+m3+m4+m5 + day) + "天");
}
else if (mooth == 7 && (day >= 1 && day <= 31))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + m5+m6 + day) + "天");
}
else if (mooth == 8 && (day >= 1 && day <= 31))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + m5 + m6+m7 + day) + "天");
}
else if (mooth == 9 && (day >= 1 && day <= 30))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + m5 + m6 + m7 +m8+ day) + "天");
}
else if (mooth == 10 && (day >= 1 && day <= 31))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + m5 + m6 + m7 + m8+m9 + day) + "天");
}
else if (mooth == 11 && (day >= 1 && day <= 30))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + m5 + m6 + m7 + m8 + m9+m10 + day) + "天");
}
else if (mooth == 12 && (day >= 1 && day <= 31))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + m5 + m6 + m7 + m8 + m9 + m10+m11 + day) + "天");
}
else
{
Console.WriteLine("输入日期有误");
}
}
else
{
Console.WriteLine("输入月份有误");
}

}
else if ((year > 1759 && year <= 9999) && !((year % 400 == 0 || (year % 100 != 0 && year % 4 == 0))))
{
Console.Write("请输入月份;");
mooth = int.Parse(Console.ReadLine());
if (mooth >= 1 && mooth <= 12)
{
Console.Write("请输入日期：");
day = int.Parse(Console.ReadLine());
int m1 = 31, m2 = 29, m3 = 31, m4 = 30, m5 = 31, m6 = 30, m7 = 31, m8 = 31, m9 = 30, m10 = 31, m11 = 30;
if (mooth == 1 && (day >= 1 && day <= 31))
{
Console.WriteLine("这是" + year + "第" + day + "天");
}
else if (mooth == 2 && (day >= 1 && day <= 28))
{
Console.WriteLine("这是" + year + "第" + (m1 + day) + "天");
}
else if (mooth == 3 && (day >= 1 && day <= 31))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + day) + "天");
}
else if (mooth == 4 && (day >= 1 && day <= 30))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + day) + "天");
}
else if (mooth == 5 && (day >= 1 && day <= 31))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + day) + "天");
}
else if (mooth == 6 && (day >= 1 && day <= 30))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + m5 + day) + "天");
}
else if (mooth == 7 && (day >= 1 && day <= 31))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + m5 + m6 + day) + "天");
}
else if (mooth == 8 && (day >= 1 && day <= 31))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + m5 + m6 + m7 + day) + "天");
}
else if (mooth == 9 && (day >= 1 && day <= 30))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + m5 + m6 + m7 + m8 + day) + "天");
}
else if (mooth == 10 && (day >= 1 && day <= 31))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + m5 + m6 + m7 + m8 + m9 + day) + "天");
}
else if (mooth == 11 && (day >= 1 && day <= 30))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + m5 + m6 + m7 + m8 + m9 + m10 + day) + "天");
}
else if (mooth == 12 && (day >= 1 && day <= 31))
{
Console.WriteLine("这是" + year + "第" + (m1 + m2 + m3 + m4 + m5 + m6 + m7 + m8 + m9 + m10 + m11 + day) + "天");
}
else
{
Console.WriteLine("输入日期有误");
}
}
else
{
Console.WriteLine("输入月份有误");
}
}
else
{
Console.WriteLine("输入年份有误");
}

}

}