#include<stdio.h>

 #include<math.h>

 void main(){

     int s=;

     double n=1.0,t=1.0,pi=;

     while(fabs(t)>1e-){    //fabs(double), abs(int)

         pi=pi+t;

         n=n+;

         s=-s;  //实现正负交替

         t=s/n;

     }

     pi=pi*;

     printf("π =%10.6lf\n",pi);

 }