就是那个1-1/3+1/5-1/7 ……，即使用双精度也只能输出没几位啊，那肯定要断开一位一位输出了，怎么做啊，头都大了，理了一点，懒得写下去了，高手给个答案
    void next(double a);
                         main()
                         {double a=1,b,c,d=-1,f,sum=1;
                         int e=1,h,i;
                         for(b=0;b<10;b++,e++)
                          {
                              f=sum*4;
                               h=f;

                              printf("sum1=%d\n",h);
                        {   a=a+2;  c=a;

                         c=(d)*(1/c);

                           d=(-1)*d ;
                           sum+=c;      }
                               i=4*sum  ;
                                  printf("sum2=%d\n",i);
                                  if(h==i)
                                 { printf("%d=%d,\n",h,i) ;
                                  a=a-4;   sum=0;  d=(-1)*d ; /*计算下一位*/
                                  {  f=sum*10;
                                      h=f;

                                    printf("sumNEXT1=%d\n",h);
                                   a=a+2;  c=a;

                         c=(d)*(1/c);

                           d=(-1)*d ;
                           sum+=c;      }    }

                              if(e%10000==0)
                             { e=1;
                               printf("yuan=%lf\n",4*sum); }
                          }
                             printf("yuan=%lf\n",4*sum);
                           getch();}
                           void next(double a)
                      {   double b,c,d=-1,f,sum=1;
                         int e=1,h,i,u;
                      if(h==i)
                      {  a=a-4;   sum=0;  d=(-1)*d ;
              a=a+2;  c=a;   c=(d)*(1/c);     d=(-1)*d ; sum+=c; i=sum1=sum*40; }

                      else
                    {a=a+2;  c=a; c=(d)*(1/c); d=(-1)*d ;  sum+=c; h=sum2=sum*40  }
                    if(h==i)
                    next(a);}
                        h=sum*10;                      }

注意数据类型的取值范围