poj 2199 Rate of Return

#include <iostream>#include <cmath>using namespace std;int main(){double rate,b[13],sum,q; int n,i,a[13],k,cae=0; cin>>n; while (n!=-1) {rate=0.000;k=6;q=0.1;  for (i=0;i<=n;i++)  cin>>a[i]>>b[i];  while (k)  {rate=rate+q+1.0;   sum=0;   for (i=0;i<n;i++)    sum=sum+b[i]*pow(rate,a[n]-a[i]+1);   rate=rate-1.0;   if (sum-b[n]>1e-8) {rate=rate-q; k--;        q=q/10;}  }  cout<<"Case "<<++cae<<": ";  printf("%.5f",rate);  cout<<endl;cin>>n;  if (n!=-1) cout<<endl; } return 0;}