基础编程题目集 7-15 计算圆周率 (15分)

#include <stdio.h>
int main()
{
    int i = 1;
    double up = 1.0f, down = 1.0f, sum = 1.0f, n;
    scanf("%lf", &n);
    do
    {
        up *= i;
        down *= (2.0 * i + 1);
        i++;
        sum += (up / down);
    } while (up / down >= n);
    printf("%.6lf", 2.0 * sum);
    return 0;
}