Fractional Knapsack

#include<bits/stdc++.h>
using namespace std;
double profit[10000],weight[1000],w_taken[10000];
int n,u;
class knapsack{
public:
    void input()
    {
        cin>>n>>u;
        for(int i=0; i<n; i++)
        {
            cin>>profit[i]>>weight[i];
        }
    }
    void solution()
    {
        selection_sort();
        int i;
        for( i =0 ;i<n; i++)
        {
            if(weight[i] > u)
                break;
            w_taken[i] = 1;
            u-=weight[i];
        }
        if(u!=0 && i<n)
        {
            w_taken[i] = u/weight[i];
        }
        profit_calculation();

    }
    void profit_calculation()
    {
        double sum = 0;
        for(int i=0; i<n; i++)
        {
            sum += w_taken[i]*profit[i];
        }
        cout<<sum;
    }
    void selection_sort()
    {
        for(int i =0; i<n-1; i++)
        {
            int max_index = i;
            for(int j = i+1; j<n; j++)
            {
                if( profit[j]/weight[j] > profit[max_index]/weight[max_index])
                    max_index = j;
            }
            swap(profit[max_index],profit[i]);
            swap(weight[max_index],weight[i]);
        }
    }
};
int main()
{
    freopen("input.txt","r",stdin);
    knapsack fk;
    fk.input();
    fk.solution();

}

/*
input:
4 70
30 10
280 40
180 20
80 10

ans 540
*/