PI的求法

1671年(J.Gregory)

π/4=1-1/3+1/5-1/7+1/9-1/11+....

#include <stdio.h>#include <string.h>#include <stdlib.h>int main(){    double pi = 0.0;    int flag, i;    int n;    while(~scanf("%d", &n))    {        pi = 1.0;        flag = 0;        for( i = 3; i < n; i += 2 )        {            pi += (flag == 0 ? -1.0 : 1.0)/i;            flag = !flag;        }        printf("%lf\n", 4.0*pi);    }    return 0;}

欧拉(Leonhard Euler)

π^2/8=1+1/3^2+1/5^2+1/7^2+.....

#include <stdio.h>#include <string.h>#include <stdlib.h>#include <math.h>int main(){    double pi = 0.0;    int n, i;    while(~scanf("%d", &n))    {        pi = 1.0;        for( i = 3; i <= n; i += 2 )        {            pi += 1.0/(i*i);        }        pi *= 8;        pi = sqrt( pi );        printf("%lf\n", pi);    }    return 0;}