求a = 1 - 1/3 + 1/5 - 1/7 + 1/9......直到被除数小于10的-6次方为止    为什么输出结果是
-92559631349317831000000000000000000000000000000000000000000000.000000


# include <stdio.h>

int main(void)
{
    int i, j = 0;
    double a;

    for (i = 1;i <= 1e6;i++)
    {
        if (i%2 == 0)
            continue;
        else
            j++;
            if (j%2 == 0)
                a -= 1.0/(double)i;
            else
                a += 1.0/(double)i;
    }
    printf("%.6lf\n", a);

    return 0;
}

int i, j = 0;
    double a=0;    //----累加变量要赋初值

另，你的程序可以简化一些：
# include <stdio.h>
int main(void)
{
    double i=1,a=0,s=1;
    do
    {
        a=a+s/i;
        s=-s;
        i=i+2;
    }while( 1/i >= 1e-6);
    printf("%lf\n", a);
    return 0;
}