static void Main(string[] args)
{
string str = Console.ReadLine();
int n = Convert.ToInt32(str);
double result = sum(n);
Console.WriteLine("阶乘的和"+result);
Console.ReadKey();
}
private static double sum(int n)
{
if (n <= 0)
{
return 0;
}
else if (n == 1)
{
return 1;//1的阶乘还是1.
}
return sum(n - 1) + product(n);
}
private static double product(int n)
{
if (n < 0)
{
return 0;
}
else if (n == 0)
{
return 1;
}
return product(n - 1) * n;
}
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