HDU 2199 Can you solve this equation?

　　　　　　　Can you solve this equation?

[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!

#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;

double cal(double x)
{
return 8*x*x*x*x+7*x*x*x+2*x*x+3*x+6;
}

int main()
{
double x,l,r;
int t;
scanf("%d",&t);
while(t--)
{
scanf("%lf",&x);
if(x<cal(0)||x>cal(100))
{
printf("No solution!\n");
continue;
}
l=0,r=100;
while(fabs(l-r)>1e-8)
{
double mid=(l+r)/2;
if(cal(mid)>x)
r=mid;
else
l=mid;
}
printf("%.4lf\n",l);
}
return 0;
}