给定一个年月值，返回上个年月值，格式为：YYYY.MM string类型

class Program
{

public string Lastmonth(string   s )
{
int  a =int.Parse(s.Substring(0,4));
int  b =int .Parse( s.Substring(4, 2));
if (b<=0||b>12 )
{
return "请输入正确地月份";
}
else if (b == 1)
{
a = a - 1;
b = 12;
return a.ToString() + b.ToString();
}
else if (b == 12 || b == 11)
{
b = b - 1;
return a.ToString() + b.ToString();
}
else
{

b = b - 1;
return a.ToString() +"0"+ b.ToString();
}

}
static void Main(string[] args)
{
Console.WriteLine("年月：");
string ss = Console.ReadLine();

Program pg = new Program();

Console.WriteLine(  pg.Lastmonth(ss));
Console.ReadLine();

}
}

转载于:https://www.cnblogs.com/xubin-747/p/5210458.html