C刷题记录-1014

 1 #include <stdio.h>
 2 
 3 unsigned long long int get_factorial (int n);
 4 
 5 int main(){
 6 
 7   int n,i;
 8   unsigned long long int SN = 0;
 9   scanf("%d",&n);
10 
11   for(i=1;i<=n;i++)
12   {
13     SN = SN + get_factorial(i);
14   }
15   printf("%lld",SN);
16   return 0;
17 }
18 
19 /*
20 需要注意数据长度，如果n很小的时候，结果是正确的，
21 但是n=20的时候，超出int的范围，所以定义成unsigned long long int
22 */
23 unsigned long  long int get_factorial (int n)
24 {
25     unsigned long long int factorial;
26     if (n==1)
27     {
28       factorial = 1;
29     }
30     else if (n>=2)
31     {
32      factorial = (unsigned long long int)n * get_factorial(n-1);
33     }
34 
35     return factorial;
36 }