hdu 2199~Can you solve the equation?～二分法求解

Can you solve this equation?

Time Limit : 2000/1000ms (Java/Other)   Memory Limit : 32768/32768K (Java/Other)
Total Submission(s) : 28   Accepted Submission(s) : 17
[align=left]Problem Description[/align]
Now,given the equation 8*x^4 + 7*x^3 + 2*x^2 + 3*x + 6 == Y,can you find its solution between 0 and 100;

Now please try your lucky.
 

[align=left]Input[/align]
The first line of the input contains an integer T(1<=T<=100) which means the number of test cases. Then T lines follow, each line has a real number Y (fabs(Y) <= 1e10);
 

[align=left]Output[/align]
For each test case, you should just output one real number(accurate up to 4 decimal places),which is the solution of the equation,or “No solution!”,if there is no solution for the equation between 0 and 100.
 

[align=left]Sample Input[/align]

2
100
-4

 

[align=left]Sample Output[/align]

1.6152
No solution!  AC_code:

#include<stdio.h>
#include<math.h>
double f(double x)
{
return 8*x*x*x*x+ 7*x*x*x + 2*x*x + 3*x + 6;
}
int main()
{
int n;
double y,mid,l,r;
scanf("%d",&n);
while(n--)
{
scanf("%lf",&y);
if(y<f(0)||y>f(100))
printf("No solution!\n");
else
{
l=0;r=100;
while(r-l>1e-10)
{
mid=(r+l)/2;
if(f(mid)<y)
l=mid+1e-10;
else
r=mid-1e-10;
}
printf("%.4lf\n",mid);
}
}
return 0;
}