Need help

[Brandon33310]

Write a program that computes the central tendencies mean (average), mode, median and the variation: variance, standard deviation and range for a set of numbers given in the data file ArsenicGroundWaterFile.txt.

The following data represent (naturally occurring) concentration of arsenic in ground water for a random sample of 102 Northwest Texas wells. Units are parts per billion.
Reference: Nichols, C.E. and Kane, V.E., Union Carbide Technical Report K/UR-1

The output should be as follows to two decimal places:

Central Tendency Variation

Mean xxx.xx Variance xxx.xx

Median xxx.xx Std. Dev xxx.xx

Mode xxx.xx Range xxx.xx


I have no idea how to do this assignment, my professor hasn't been of any help. Please help me get started.

[Chervil]

Start by reading the values from the file into an array. Do you know how to do that?

[Brandon33310]

No I am not familiar with how the do that.

[mbozzi]

http://www.cplusplus.com/doc/tutorial/files/

[Brandon33310]

Okay i read over that and it helped some but i'm still very confused.

[mbozzi]

Could you post what you have?

[Brandon33310]

I just have it right now to where it will read the file and display what is in it.

#include <iostream>
#include <fstream>
#include <cmath>
#include <cstdlib>


using namespace std;

ifstream myFile;
double Value;
int main()
{



    ifstream myfile("numbers.txt");
        if(myfile.is_open()){

                while(myfile >> Value){

                    cout << Value << endl;
                }
        }



  }

[Chervil]

After that you need to store the values, the C++ way is to use a std::vector but you may be expected to use an array.

By the way, avoid global variables - lines 9 and 10 in above code, better removed and declared locally instead.

1. use a vector

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

using namespace std;

int main()
{   
    // Open file and check it is open
    ifstream myfile("numbers.txt");
    if (!myfile)
    {
        cout << "could not open input file\n";
        return 1;
    }
    
    // read all values from file into a vector
    vector<double> data;
    double value;
    while (myfile >> value)
    {
        data.push_back(value);
    }
    
    // Output contents of vector
    cout << "Number of values: " << data.size() << '\n';
    for (size_t i = 0; i < data.size(); i++)
    {
        cout << data[i] << endl;
    }
        
    
  }

2. same functionality (more or less) using an array instead:
I added more comments because arrays require more care and attention.

#include <iostream>
#include <fstream>
#include <cmath>
#include <cstdlib>

using namespace std;

int main()
{   
    // Open file and check it is open
    ifstream myfile("numbers.txt");
    if (!myfile)
    {
        cout << "could not open input file\n";
        return 1;
    }
    

    // Allocate an array - estimate size required
    const int SIZE = 1000; // Maximum number of values
    double data[SIZE];     // define an array we hope is large enough
    int count = 0;         // keep track of how many values are stored.
    
    // read all values from file into an array
    double value;
    while (count < SIZE && myfile >> value) // while array is not full, read a value
    {
        data[count] = value;  // store it
        count++;              // increaase count
    }
    
    // Output contents of array
    cout << "Number of values: " << count << '\n';
    for (int i = 0; i < count; i++)
    {
        cout << data[i] << endl;
    }
        
    
  }

Once you reach this stage, it's time to move on to writing separate functions to generate the each of the various statistics required.