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#include <algorithm>
#include <cmath>
#include <fstream>
#include <iostream>
#include <vector>

double calculateArea( double radius )
{
    return M_PI * radius * radius;
}

int main()
{
    std::ifstream inputFile( "promienie.txt" );
    std::ofstream outputFile( "wynik.txt" );

    std::vector< double > areas;

    if( inputFile.is_open() )
    {
        double radius;
        while( inputFile >> radius )
        {
            double area = calculateArea( radius );
            areas.push_back( area );
        }
        inputFile.close();
    }
    else
    {
        std::cerr << "Nie mozna otworzyc pliku promienie.txt\n";
        return -1;
    }

    std::sort( areas.begin(), areas.end() );

    if( outputFile.is_open() )
    {
        for( const auto& area : areas )
        {
            outputFile << area << '\n';
        }
        outputFile.close();
    }
    else
    {
        std::cerr << "Nie mozna otworzyc pliku wynik.txt\n";
        return -1;
    }

    std::cout << "Policzono pola kol i zapisano do pliku wynik.txt\n";

    return 0;
}