7.6

#include<stdio.h>int x,b,cj,sum=0;int fact(int i){    for(x=1;x<=i;x++)    {       cj=1;    for(b=1;b<=x;b++)    {       cj*=b;          }       sum+=cj;    }       return sum; }int main(){    int n;      printf("请输入一个数n:");    scanf("%d",&n);    fact(n);    printf("%d\n",sum);    return 0;}