c++二分求解

#include<stdio.h>
using namespace std;
double a, b, c, l, r, mid;
double p(double x)
{
	double s = 0;
	s += b / x;
	x = x * mid / 100;
	return s;
}
int main()
{
	scanf("%lf%lf%lf", &a, &b, &c);
	r = 1000;
	while(l + 1 < r)
	{
		mid = (l + r) / 2;
		double t = mid / 100;
		if(p(t) > a)
		{
			l = mid;
		}
		else
		{
			r = mid;
		}
	}
	printf("%.1lf", r);
}