1,
1 #include <stdio.h> //错; 2 main() 3 { 4 unsigned long long int n,sum; 5 scanf("%llu",&n); 6 sum=(1+n)*n/2; 7 printf("%llu",sum); 8 return 0; 9 } 10 11 12 #include <stdio.h> //正确; 13 int main() 14 { 15 unsigned long long int n,sum; //计算机计算时候避免计算出错,奇数偶数/2不一样,当答案一直错误时候往往是输出问题; 16 scanf("%llu",&n); 17 if(n % 2 == 0) 18 sum = n / 2*(n + 1); 19 else 20 sum = (n + 1) / 2 * n; 21 printf("%llu",sum); 22 }