C语言编程题，计算输出以下数列前20项的和，结果保留三位小数，1，-1⼀3，1⼀5，-1⼀7，1⼀

#include 

int main()
{
    double ans = 0, temp;
    int i;
    for (i = 1; i <= 20; ++i){
        temp = 1.0/(double)(2*i-1);
        if ((i-1)%2 == 1){
            temp *= -1;
        }
        ans += temp;
    }
    printf ("%.3f\n", ans);
}

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