利用π/2求π的近似值

#include <stdio.h>
int main()
{
    double dx = 1, dy = 1, n = 0;
    double d = 1, sum = 1;

    while (d >= 1e-6)
    {
        dx *= ++n;
        dy *= (2 * n + 1);
        d = dx / dy;
        sum += d;
    }
    sum *= 2;
    printf("%lf", sum);

    return 0;
}