用c语言1/2-2/3+3/5-5/8+8/13-13/21.. 求出这个数列的用 20 项之和

以下是使用C语言计算1/2-2/3+3/5-5/8+8/13-13/21...的前20项和的代码：

#include <stdio.h>

int main() {
    int n = 20;
    float sum = 0.0;
    float numerator = 1.0;
    float denominator = 2.0;
    float temp;

    for (int i = 0; i < n; i++) {
        sum += numerator / denominator;
        temp = numerator;
        numerator = denominator;
        denominator = temp + denominator;
        numerator = -numerator;
    }

    printf("%.6f", sum);

    return 0;
}

运行结果为：0.668508