C语言数列求和题：函数fun是根据输入n和x，求下面分母为n以内(包含n)的非素数构成的数列的和

#include<stdio.h>
#include<stdlib.h>
double fun(int n,double x)
{
/***********************Begin************************/


/***********************End*************************/
}
int main()
{
    int n;
    double s,x;
    FILE *in,*out;
    printf("输入n和x:");
    scanf("%d %lf",&n,&x);
    s=fun(n,x);
    printf("%lf\n",s);
    /*****************/
    in=fopen("in2019-2-2-3.dat","r");
    out=fopen("out2019-2-2-3.dat","w");
    while(!feof(in))
    {
        fscanf(in,"%d %lf",&n,&x);
        fprintf(out,"%lf\n",fun(n,x));
    }
           fclose(in);
           fclose(out);
    system("pause");
    return 0;    
}

供参考：

#include <stdio.h>
#include <stdlib.h>
double fun(int n, double x)
{
    /***********************Begin************************/
    double s = 0, t = 1.0;
    int i, j, k = 0, * a = (int*)malloc(sizeof(int) * n);
    a[k++] = 1;
    for (i = 1; i <= n; i++) {
        for (j = 2; j * j <= i; j++) {
            if (i % j == 0) {
                a[k++] = i;
                break;
            }
        }
    }
    for (i = 0; i < k; i++) {
        t *= x;
        i % 2 == 0 ? s += t / a[i] : s -= t / a[i];
    }
    free(a);
    return s;
    /***********************End*************************/
}
int main()
{
    int n;
    double s, x;
    FILE* in, * out;
    printf("输入n和x:");
    scanf("%d %lf", &n, &x);
    s = fun(n, x);
    printf("%lf\n", s);
    /*****************/
    in = fopen("in2019-2-2-3.dat", "r");
    out = fopen("out2019-2-2-3.dat", "w");
    while (!feof(in))
    {
        fscanf(in, "%d %lf", &n, &x);
        fprintf(out, "%lf\n", fun(n, x));
    }
    fclose(in);
    fclose(out);
    /***************/
    system("pause");
    return 0;
}