For nesting

question

Please calculate the sum of the factorials of N numbers

think

先把问题分为两个部分

1. The factorial of N

	那么N的阶乘应该是从1乘到N
	也就是说for循环

		int sum=1;
		for (int i = 1; i <= n; ++i)
        {
    
    
            sum2 = sum2 * i;
        }

2. Add N factorials

	那么N个数相加也应写一个for循环

		for (int i = 1; i <= n; ++i)
        {
            sum1 = sum2 +i ;
        }

3. How to nest

	先来思考结构：
	必然是要有两个for，一个相加，一个求阶乘
	那么先来列举几个
	当n=2：
	那么就是1！+2！，直接写代码就该是

//The first time is 1!
int sum=1;
for (int i = 1; i <= 1; ++i)
{
sum2 = sum2 * i;
}
//The second time is 2!
int sum=1;
for (int i = 1; i <= 2; ++i)
{ sum2 = sum2 * i; } Then add the sum2 of the two. Then just add up the separate codes, but it should be noted that the sum2 here should be reset to 1 every time, because the calculation is the factorial of the inner layer, and the value of sum2 should be added to the sum1 every time, that is, for ( int i = 1; i <= n; ++i) { sum2=1 for(){}; sum1 = sum2 +i ; }

the code

#include<stdio.h>
int main()
{
    
    
  long long a,sum1=0,sum2=1;
  scanf("%lld", &a);
  for (int i = 1; i <= a; ++i)
  {
    
    
      sum2 = 1;
      for (int j = 1; j <= i; ++j)
      {
    
    
          sum2 = sum2 * j;
      }
      sum1 = sum1 + sum2;
  }
  printf("%lld", sum1);
  return 0;
}