int main()
{
int fac(int n);
int n;
int y;
printf("input an integer number:");
scanf("%d", &n);
y = fac(n);
printf("%d! = %d \n",n, y);
return 0;
}
int fac(int n)
{
int f=0;
if (n< 0)
{
printf("DATA ERROR！\n");
}
else if (n == 0 || n == 1)
{
f = 1;
}
else
f = fac(n - 1)*n;
return f;
}