Question regarding using eof in a while loop.

[Tellumendil]

My professor assigned us a project that requires us to use "eof" (quotation marks for emphasis) in a "while" loop. I have done quite a bit of research and realize why I have the issue I will relate in a bit. However, using "eof" is part of what will determine my grade, meaning that even though I am aware that I could achieve what I need using other code, I must use eof in this case.

I also understand that there are other more elegant, and effective, ways to write the program that will accomplish what I need, but that is a battle for another day. I need to focus on my issue with "eof" for now.

When using "eof", I have noticed that my program outputs the last set of data twice. As I understand, the loop checks for eof only after it reads the file, which causes it to repeat the last set of data.

What I need to accomplish is to use "eof" without repeating the last set of data twice in order to accomplish what my professor expects.

The code I wrote follows below.

Thanks in advance for your assistance.

#include <iostream>
#include <fstream> // File stream (output and input to a file).
#include <iomanip> // Output and input manipulation.

using namespace std;

int main()
{
// char variables will be set to up to 20 characters.
ifstream inData; // Variable that will store input file stream data.
ofstream outData; // Variable that will store output file stream data.
char exit; //Variable that will be used to terminate program.
char fiName [20]; // Variable that will store the name of the file the user creates.
char firstName [20]; // Variable that will store the first names.
char lastName [20]; // Variable that will store last names.
double gradeA, gradeB, gradeC, gradeD, gradeE; //variables that will store grades.
double average; // Variable that will be used to calculate average grade.
int roundedAverage; // Variable that will be used to round calculated average to an integer.
int counter1; // Variable to start for loop that will request user to input data 5 times.
int counter2=0; // Variable to start while loop that will check user for invalid input.
                // It is set to begin at 0 to allow for 3 attempts.

// Request user input file name to create file.
cout << "\n Please enter a file name to store information and press enter: ";
cin >> fiName;
cout << "\n You set your file name to: " << fiName << "\n";

    outData.open (fiName); //Open file created by user to write into it.
        //Request data from user.
        cout << "\n\n Enter first name and press enter: ";
        cin >> firstName;
        cout <<"\n Enter last name and press enter: ";
        cin >> lastName;
        cout << "\n Enter five grades separated by a space and press enter: ";
        cin >> gradeA >> gradeB >> gradeC >> gradeD >> gradeE;
        // Write data entered by user into the file.
        outData << firstName << " " << lastName << " ";
        outData << gradeA << " " << gradeB << " " << gradeC << " " << gradeD << " " << gradeE << " ";
    for (counter1=0;counter1<4;counter1++) //For loop to ask and store names and grades four more times.
    {
        //Request data from user.
        cout << "\n\n Enter another first name and press enter: ";
        cin >> firstName;
        cout <<"\n Enter another last name and press enter: ";
        cin >> lastName;
        cout << "\n Enter five grades separated by a space and press enter: ";
        cin >> gradeA >> gradeB >> gradeC >> gradeD >> gradeE;
        // Write data entered by user into the file.
        outData << firstName << " " << lastName << " ";
        outData << gradeA << " " << gradeB << " " << gradeC << " " << gradeD << " " << gradeE << " ";
    }
    outData.close (); // Close file created by user once it contains all requested data.

// Request user to input file name to open file.
cout << "\n\n Enter file name to read and press enter: ";
cin >> fiName;

    inData.open(fiName); //Open file created by user to read from it.
        // While loop to check for incorrect file name.
        // It will display an error message, up to three times, before terminating
        // if the user conitnues to enter the wrong file name.
        while (!inData&&counter2<2)
        {
            cout << "\n File not found." << endl;
            cout << "\n Reenter file name: ";
            cin >> fiName;
            inData.open (fiName);
            counter2++;
        }
            // if statement to terminate program in case user enters incorrect
            // file name three times.
            if (!inData)
            {
                cout << "\n File not found. Program Terminated.";
                /*On my notes, a break; statement followed the statement above, but the
                compiler told me that I could not use break with an if statement. My
                solution to terminate the program at this point was to use the three
                lines of code below.*/
                cout << "\n\n To exit the program, enter any key and press enter: ";
                cin >> exit;
            }

        while (!inData.eof())
        {
        // Read data entered by user from file in the same order it was stored.
        inData >> firstName >> lastName >> gradeA >> gradeB >> gradeC >> gradeD >>gradeE;
            cout << "\n Name: " << firstName << " " << lastName;
            cout << "\n Grades: " << gradeA << ", " << gradeB << ", " << gradeC << ", ";
            cout << gradeD << ", " << gradeE;

        // Calculate and display average grade.
        average=(gradeA+gradeB+gradeC+gradeD+gradeE)/5.0; //Calculate average grade.
            cout << "\n " << firstName << " " << lastName << "'s" <<" average grade is: ";
            cout << average; //sets output width to six characters.
        roundedAverage=average+0.5; // Round average grade to an integer.
            cout << "\n Rounded and final grade is: " << roundedAverage << "\n\n";

        }
    inData.close();

    cout << "\n To exit the program, enter any key and press enter: ";
    cin >> exit;

    return 0;
}

I tried placing:

 if (inData.eof())
break;

Just before the end of the loop, hoping it would check then and not repeat the last line, but it did not work.

[48T7M4Gy]

Try using this, otherwise wait around because you are about to experience an avalanche of peeks and reasons why you shouldn't use it (and quite rightly so as a general rule) but that doesn't help you much if you have an uber-dominant lecturer.

http://www.cplusplus.com/reference/ios/ios/eof/

http://stackoverflow.com/questions/21647/reading-from-text-file-until-eof-repeats-last-line

[jlb]

While in most circumstances using eof() to control input loops is a bad idea it is possible to use eof() if done properly.

What you will need to do is pre-read the information before the loop, the at the end of the loop read another time:

    ifstream fin("datafile.txt");
    // You must insure the file opened correctly! A failure of opening the file will not be caught by just testing for eof.
    if(!fin)
    {
       cout << "Input file failed to open.\n";
       return 1
    }
    // Read a set of data before the loop.
    fin >> data;
    // Use fail() to insure that there are no read failures.
    while(!fin.eof() || fin.fail())
    {
        // Do what ever with the data here.

        // At the end of the loop read another set of data.
        fin >> data;
    }

[Tellumendil]

Got it, and it worked.

Thank you all for the help. I am still very new to programming in general and would love to learn how to do things the most effective way. As I said before, I realize that there are many things I could do to improve the code, but I simply don't know enough to do it at the moment, and I also had no other option but to use the feature my professor expected.

I am glad that I found these forums.

[48T7M4Gy]

Have a look at the tutorials on this site and here is the section on input and output from files as a start.

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