//用二分法求方程x2-x-1=0的正根，要求準(zhǔn)確到小數(shù)點(diǎn)后第一位
 	#include<iostream.h>
    #include<iomanip.h>
int main()
{
	float left=0,right;      //左邊界初始值為0 
	float m;
	float mid;
 float r1=1000,r2=100;    //賦值原則，保證for語句至少執(zhí)行兩次
	for(m=0;;m++) if((m-1)*m-1>0) break;  //自動搜尋右邊界 
	right=m; 
	for(int a=0;;a++) 
	{
		mid=float(left+right)/2;
		if(r1-r2<0.05&&r2-r1<0.05)
		{
			cout<<setiosflags(ios::fixed)<<setprecision(1)<<float(r2+r1)/2<<endl;				
			break;
		} else if((mid-1)*mid-1>0) {
			right=mid;
			if(a%2==0) r1=mid;
			else r2=mid;
		} else if((mid-1)*mid-1<0) {
			left=mid;
			if(a%2==0) r1=mid;
			else r2=mid;
		}
	}
	return 0;
}