刚刚学了循环，1到n的求和与阶乘

//求和
int a = Convert.ToInt32(Console.ReadLine());
int c = 0;
for (int b = 0; b <= a; b++)
{
c = c + b;

}
Console.Write(c);

//阶乘
int a = Convert.ToInt32(Console.ReadLine());
int end = 1;
for (int b=1; b<=a;b++ )
{
end = end * b;

}
Console.Write(end);