c语言编程求数列的1/1-1/3+1/5-1/7+1/9……前20项的累计和？

Question

得到的答案是1.00，错的。但是，错在哪了？求助
#include<stdio.h>
int main()
{
int num = 1, sign = 1, term = 1;
double sum = 1.00;
while (num <= 20)
{
sign = -sign;
term = term + 2;
sum = sum + (sign / term);
num++;
}
printf("前20项和=%0.2f", sum);
}

Answer 1

#include <stdio.h>

int main()

{

    int num = 1, sign = 1, term = 1;

    double sum = 1.00;

    while (num <= 20)

    {

        sign = -sign;

        term = term + 2;

        sum = sum + ( (double) sign / term);

        num++;

    }

    printf("前20项和=%0.2f", sum);

}