Having trouble calculating + printing max/min values

[BenW]

Hi all,

I'm trying to write a program that reads the data below from an input file, planetsinput.txt, computes the density for each planet and prints the answer to an output file, planetsoutput.txt, along with the highest and lowest values.

Currently I have everything working except for the fact that I'm getting an incorrect output for max and min.

Any help would be much appreciated.

Thanks!

INPUT FILE DATA

Mercury		2440		3.30e+23
Venus		6052		4.87e+24
Earth		6371		5.97e+24
Mars		3390		6.39e+23
Jupiter		69911		1.90e+27
Saturn		58232		5.68e+26
Uranus		25362		8.68e+25
Neptune		24622		1.02e+26
Pluto		1186		1.31e+22

CODE

#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>

using namespace std;

void Input();

int main()	{
    Input();
    return(0);
}


void Input()	{
    
    string Planet[9];
    double Radius[9];
    float Mass[9];
    const double pi = 3.14159;
    int i=0;
    
    double volume;
    double density[i];
    
    double min_x;
    min_x = density[0];
    
    double max_x;
    max_x = density[0];
    
    ifstream fin;
    ofstream fout;
    
    fout.open("planetsoutput.txt");
    
    fin.open("planetsinput.txt");
    if(fin.fail())	{
        cerr << "couldn’t open the file!" << endl;
        exit(1);
    }
    
    for (i=0; i<9; ++i)	{
        fin >> Planet[i] >> Radius[i] >> Mass[i];
        
        volume = ((4)*(pi)*(Radius[i]*Radius[i]*Radius[i]))/(3);
        density[i] = Mass[i]/volume;
        
        fout << Planet[i] << endl;
        fout << "--------" << endl;
        fout << "Radius: " << Radius[i] << endl;
        fout << "Mass: " << Mass[i] << endl;
        fout << "Volume: " << volume << endl;
        fout << "Density: " << density[i] << "\n\n" << endl;
    }
    
    for (int k=0; k<=8; ++k)	{
        if (density[k] > density[!k])
            max_x = density[k];
    }
    fout << "The max is " << max_x << endl;
    
    for (int k=0; k<=8; ++k)	{
        if (density[k] < density[!k])
            min_x = density[k];
    }
    
    fout << "The min is " << min_x << endl;
    
    
    fin.close();
    fout.close();
}

OUTPUT FILE DATA

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72

Mercury

Radius: 2440 Mass: 3.3e+23 Volume: 6.08496e+10 Density: 5.42321e+12 Venus -------- Radius: 6052 Mass: 4.87e+24 Volume: 9.28507e+11 Density: 5.24498e+12 Earth -------- Radius: 6371 Mass: 5.97e+24 Volume: 1.08321e+12 Density: 5.51142e+12 Mars -------- Radius: 3390 Mass: 6.39e+23 Volume: 1.63188e+11 Density: 3.91574e+12 Jupiter -------- Radius: 69911 Mass: 1.9e+27 Volume: 1.43128e+15 Density: 1.32748e+12 Saturn -------- Radius: 58232 Mass: 5.68e+26 Volume: 8.27129e+14 Density: 6.86713e+11 Uranus -------- Radius: 25362 Mass: 8.68e+25 Volume: 6.83343e+13 Density: 1.27023e+12 Neptune -------- Radius: 24622 Mass: 1.02e+26 Volume: 6.25257e+13 Density: 1.63133e+12 Pluto -------- Radius: 1186 Mass: 1.31e+22 Volume: 6.98783e+09 Density: 1.87469e+12 The max is 5.51142e+12 The min is 1.87469e+12

[keskiverto]

Can you explain the density[!k]?

[BenW]

Well I was trying to do something like

        if (density[k] > density[not k])
            max_x = density[k];
    }

i suppose i might not be able to do that operation.. but even then I'd wonder why it's still giving me some output.

Thoughts?

[keskiverto]

The ! takes a bool operand. Therefore, the k is implicitly converted first to bool. The ! negates the boolean value. Then the bool is converted back to integral value in order to do the array indexing.


However, wouldn't it be more logical to compare to max_x, if the intent is to determine whether max_x has to be updated?


There is also the other way:
max_x = *std::max_element( density, density + ???? );

The ???? above is, because your line 25 is bad. Are you really creating a 0 element long array?