while (true)
{
Console.WriteLine("请输入行李重量");
double k = Convert.ToDouble(Console .ReadLine ());
if (k >= 0 && k < 50)
{
double m;
m = k * 0.25;
Console.WriteLine("您的运费为"+m+"元");
}
else if (k >= 50)
{
double m;
m = k * 0.25 + (k - 50) * 0.4;
Console.WriteLine("您的运费为" + m + "元");
}
else
{
Console.WriteLine("请输入正确的重量");
}