HDU1009 fatmouse ' Trade (classic greedy)

#include <stdio.h>
#include <algorithm>
#include <iostream>

using namespace std;
struct food
{
    Double p;//value
    double w;//weight
    double r;//price-to-weight ratio
} a[2000];

BOOL Bigger (food A,food b)
{
    return a.r>b.r;//comparison function, return cost-effective
}

double sum;
int main ()
{
    freopen ("In.txt", "R", stdin);
    int m,n,i;
    while (scanf ("%d%d", &m,&n)!=eof)
    {
        if (m==-1&&n==-1) break;
        for (i=0; i<n; i++)
        {
            scanf ("%lf%lf", &A[I].P,&A[I].W);
            A[i].r= (double) a[i].p/a[i].w;
        }
        Sort (a,a+n,bigger);
        sum=0;//the existing value in the package for
        (i=0; i<n; i++)
        {
            if (M>A[I].W)
            {
                sum+=a[i].p;
                M-=A[I].W;
            }
            else
            {
                sum+=a[i].r*m;
                m=0;
                break;
            }
        }
        printf ("%.3lf\n", sum);
    }
    return 0;
}