Code to copy

//Include the needed header files
#include <fstream>
#include <iostream>
#include <iomanip>
#include <string>
#include <cmath>
using namespace std;

//Function declarations
unsigned int readDataFromFile(ifstream &fInput, double &P, double &i, int &t);
double calculateFutureValue(double P, double i, int t);
void writeDataToOutputFile(ofstream &fOutput, double F, double P, double i, int t);

//Driver function
int main()
{
    //Declare the needed variables
    ifstream fInput;
    ofstream fOutput;
    string nameOfInputFile, nameOfOutputFile;
    double P, i, F;
    int t;
    unsigned int result;

    //Set precision
    cout << setprecision(2) << fixed << showpoint;

    //Prompt for input file
    cout << "Enter the name of the input file: ";

    //Read input file name
    cin >> nameOfInputFile;

    //Open the input file
    fInput.open(nameOfInputFile.c_str());

    //Check condition
    if (fInput.fail())
    {
        //Error message
        cout << "File \"" << nameOfInputFile << "\" could not be opened" << "\n";
    }

    //Otherwise
    else
    {
        //Open a file for writing output
        fOutput.open("output.xls");

        //Write to output file
        fOutput << "Future Value" << "\t" << "Present Value" << "\t" << "Monthly Interest" << "\t" << "Months" << endl;

        //Loop to iterate and compute
        while (true)
        {
            //Assign result with the function return
            result = readDataFromFile(fInput, P, i, t);

            //Check condition
            if (result == 1)
            {
                //Assign F with function return
                F = calculateFutureValue(P, i, t);

                //Function call
                writeDataToOutputFile(fOutput, F, P, i, t);
            }

            //Check condition
            else if (result == 2)
            {
                //Display
                cout << P << " " << i << " " << t << endl;

                //Display
                cout << "One or more of the above values are not greater than zero\n";

                //Continue
                continue;
            }

            //Otherwise
            else
            {
                //Close input file
                fInput.close();

                //Close output file
                fOutput.close();

                //Stop
                break;
            }
        }
    }

    //Pause
    cin.get(); cin.get();

    //Return
    return 0;
}

//Function definition - readDataFromFile()
unsigned int readDataFromFile(ifstream &fInput, double &P, double &i, int &t)
{
    //Check condition
    if (fInput >> P >> i >> t)
    {
        //Check condition
        if (P <= 0 || i <= 0 || t <= 0)

            //Return
            return 2;

        //Otherwise
        else

            //Return
            return 1;
    }

    //Otherwise
    else
    {
        //Return
        return 0;
    }
}

//Function definition - calculateFutureValue()
double calculateFutureValue(double P, double i, int t)
{
    //Compute F
    double F = (P)*pow(1 + (i / 100), t);

    //Return F
    return F;
}

//Function definition - writeDataToOutputFile()
void writeDataToOutputFile(ofstream &fOutput, double F, double P, double i, int t)
{
    //Write to output file
    fOutput << F << "\t\t" << P << "\t\t" << i << "\t\t\t" << t;
}