求大神解答，这个要怎么写

#include <stdio.h>
#include <stdlib.h>

double fun1(int n)
{
    int i, k = -1;
    double sum = 0;
    long a = 1, b = 2, t;

    for(i = 1; i <= n; i++)
    {
        k = k * -1;
        sum += (double)k * a / b;

        printf("%c %ld/%ld ", k < 0 ? '-' : '+', a, b);
        t = a;
        a = b;
        b = t + b;
    }

    return sum;
}
int main()
{
    int n;
    printf("计算1/2-2/3+3/5-5/8……\n输入n：");
    scanf("%d", &n);

    printf("= %lf ", fun1(n));

    system("pause > nul");
    return 0;
}