程序代码：

# include <stdio.h>
# include <math.h>
int main(void)
{
    double sum = 0;       //定义sum
    int i = 1;

    while(1)               //循环
    {
        sum = sum + 1.0/i;
        i = i + 2;
        i = -i;
        if(fabs(1.0/i)<1e-6)break;      //如果绝对值小于10-6，结束循环
    }

    printf("π=%lf", sum*4);          //输出π

    return 0;
}