How can I return an error code and format the table in this program?

CSCI-15 Assignment #1 — Functions and files review (40 points), due September 9, 2013.

Write a program to read the coefficients of a series of quadratic equations from a text file and print the associated roots, or appropriate errors if there are no real roots, to another text file. The coefficients of a quadratic are the a, b and c of an expression of the form ax2 + bx + c, and the roots are the values of x that make the value of the expression 0.

If a == 0, the formula describes a line, and you may ignore any roots (just say it isn’t a quadratic and has no solutions), and if (b2-4ac) < 0 it has only complex roots.

Write a function to read one set of values from the file, using reference parameters to get the values out of the function and the function’s return value to indicate whether or not the function was able to correctly read three values. The data error you must deal with here is too few values on the line, e.g., the line has an a value only and no b or c. You may assume that the last line in the file is the only one with an error (if any error exists), and your function should return an error code to make the program stop processing after this error. This restriction allows you to use stream extraction to read the file, rather than reading lines and parsing them yourself. If you want to try doing this, that’s O.K., but get it working the easy way first.

Write a second function to calculate the roots, taking the coefficients through value parameters and giving back the roots (if they exist) via reference parameters. Use the return value to indicate success at calculating roots (0), no solution (-1) or complex roots (-2). Do not call this function if you have a data error on input.

Write a third function to print a reasonably formatted table (one row per call from the main loop) of the coefficients, and either the roots or (different) messages indicating the various error conditions. It must print appropriate error messages in the cases of a data error on input and either no solution or complex roots from the calculation function. Your table must have a reasonable title line (or lines) with legends describing what things are below it in the columns, and this table's title line must be printed inside the print function. The function must know if it is being called for the first time (or not) to print the title line. You may not pass this information into the print function from main(). The print function MUST do this itself. Always print the coefficients unless you have a read error. You must align the values in the columns in a reasonable way (if you can't align the decimal points in the columns, that's OK). Don't worry about page breaks and new title lines if the output runs beyond one page.

Your main() function will prompt for the file names (hold the names in C-strings), open the input and output files, check for file open errors appropriately, loop over the input file reading coefficients, calculating roots, and printing results to the output file until either end-of-file or error on input, and then close all the files and exit. You may make no assumptions about how many coefficients are in the input file (e.g., you may not hold the values in arrays and process them after reading them all).
You may not use any global variables in this program. Your variables must be declared appropriately within the functions where needed; and passed to other functions as either reference or value parameters as appropriate. Your functions will indicate any problem they encounter by returning a value to main(), where the error must be handled appropriately. Your functions outside main() may do only the task assigned to them, and must do that entire task. For example, you may not check for a == 0 within main and only call the calculation function if a is not zero. Think carefully about what data you need inside each function, and what must be passed around between functions.

Each correct input line will comprise three real values of the form
[optional sign][digits][decimal point][digits], or
[optional sign][digits] if integer.
The last input line might have fewer values. For example, your data file might look like this:

1 1 1
1.2 -2.3 0.4
-2 -3 -4
+0 -2 8.85
2.345           (error — only one data point)

These data are available as in the file quadratic1.txt.

Here is my solution:

#include<iostream>
#include<iomanip>
#include<string>
#include<fstream>
#include<cmath>
using namespace std;

int quadValues(ifstream&, double&, double&, double&);
int calcRoots(double, double, double, double&, double&);
int numTable(ofstream&, double, double, double, double&, double&);

// Read each set of values from the input file.
int quadValues(ifstream &inputFile, double &x, double &y, double &z)
{
    int value;  
    double root1, root2;
    string fileName;
    ofstream outputFile;

    // Get the name of the input file from the user.
    cout << "Enter the name of the file: ";
    cin >> fileName;

    // Open the file.
    inputFile.open(fileName.c_str());

    // If successfully opened, process the file data.
    if(inputFile)
    {
        // Open the output file named quadratic table.txt.
        outputFile.open("quadratic result.txt");

        // Indicate whether function read three values.
        while(inputFile >> x >> y >> z)
        {
            calcRoots(x, y, z, root1, root2);
            numTable(outputFile, x, y, z, root1, root2);
        }
        // Close the output file.
        outputFile.close();
        // Close the file.
        inputFile.close();
    }
    else
    {
        // Display the error message
        cout << "There was an error opening the input file.\n";
    }
    return 0;
}

// Calculate the roots
int calcRoots(double a, double b, double c, double &root1, double &root2)
{
    // If a is 0, there is no solution.
    if(a == 0)
    {
        return -1;
    }
    // If discriminant is less than 0, there are complex roots.
    else if((b*b-4*a*c) < 0)
    {
        return -2;
    }
    // Otherwise, return the real numbers.
    else
    {    
        root1 = (-b+sqrt((b*b)-(4*a*c)))/(2*a);
        root2 = (-b+sqrt((b*b)-(4*a*c)))/(2*a);    
        return 0;
    }
}

// Print results on a formatted table
int numTable(ofstream &outputFile, double a, double b, double c, double &root1, double &root2)
{
    // Write the output to the file.
    outputFile << "a" << setw(7) << "b" << setw(6) << "c" << setw(14)
    << "Root 1" << setw(12) << "Root 2" << setw(13) << "Errors" << endl;
    outputFile << "---------------------------------------" 
    << "--------------" << endl;
    outputFile << a << setw(8) << b << setw(8) << c << setw(14) << root1
    << setw(14) << root2 << endl;

    return 0;
}

// Call every function.
int main()
{
    ifstream inputFile;
    double x, y, z;

    quadValues(inputFile, x, y, z);

    return 0;
}

Here is my output:

a      b     c        Root 1      Root 2       Errors
-----------------------------------------------------
1       1       1  1.13296e-317  2.51147e-307
a      b     c        Root 1      Root 2       Errors
-----------------------------------------------------
1.2    -2.3     0.4       1.72323       1.72323
a      b     c        Root 1      Root 2       Errors
-----------------------------------------------------
-2      -3      -4       1.72323       1.72323
a      b     c        Root 1      Root 2       Errors
-----------------------------------------------------
0      -2    8.85       1.72323       1.72323

I'm almost there, but in the function quadValues(), I'm not sure how to return an error code if there are too few value on the line, which is the fifth line in the data file. I need to know how to return no solution, complex roots, and real solutions in the function calcRoots(). Also, I'm not sure how to format the table correctly in the function numTable(). What do I need to fix in these functions?