#include <iostream>     
#include <cmath>      
using namespace std;    
int main()              
{
    int ct = 1 , i ;
    double pi0 , pi1 , total = 0 , diff = 10 , MaxError ;
    cout << "输入MaxError ==>" ;
    cin >> MaxError ;
    pi0 = sqrt ( 1 * 6 ) ;     
    while ( MaxError < diff ){ 
          ct = ct + 1 ;
          for ( i = 1 ; i <= ct ; i++ ){     
              total = total + (1 / pow ( i , 2.0 )) ;
              }
          pi1 = sqrt ( total * 6 ) ;
          total = 0 ;       
          diff = pi1 - pi0 ; 
          pi0 = pi1 ;        
    }                  
    pi0 = pi1 - diff ; //所以pi0=pi1-diff 
    cout << "ct = " << ct << endl;
    cout << "preApprox = " << pi0 << endl;
    cout << "newApprox = " << pi1 << endl;
    cout << "diffApprox = " << diff << endl;
    system("pause") ;  
return 0 ;
}