Arrays problem

[nedim]

Here is my code which compares answers in two files and outputs correct answer and wrong. The problem is why I can't output all elements of array inside function.

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

using namespace std;

//prototypes of functions
void openAnswerKeyFile(ifstream&);

// put into array
void readAnswerKeyFile(string answerArray[], ifstream&);

void openStudentFile(ifstream&);
//void openOutputFile(ofstream&);

void readStudentAnswers(string studentAnswersArray[], ifstream&);
int compare(string answers[], string studentAnswersArray[], bool missedQuestions[]);

int main() {

    // creates object answerFile of type ifstream
    string answers[25];
    string studentAnswersArray[27];
    bool missedQuestions[25] = {false};
    
    ifstream answerFile;
    openAnswerKeyFile(answerFile);

    ifstream studentAnswers;
    openStudentFile(studentAnswers);

    //ofstream outputFile;
    //openOutputFile(outputFile);

    readAnswerKeyFile(answers, answerFile);
    readStudentAnswers(studentAnswersArray, studentAnswers);
   int numberOfWrong= compare(answers, studentAnswersArray, missedQuestions);


    //outputFile.close();
    return 0;
}

// opens answer file

void openAnswerKeyFile(ifstream& answerFile) {

    // filenames are declared as an array because 
    // ifstream class method open requires char as parameter

    char answerFilename[] = "Answer Key 1.txt";
    char answerFilename2[] = "Answer Key 2.txt";
    char answerFilename3[] = "Answer Key 3.txt";
    string userInput = "";

    while (userInput != answerFilename && userInput != answerFilename2 && userInput != answerFilename3) {
        cout << "Enter answer key filename: " << endl;
        getline(cin, userInput);
    }

    // take from user number of file. Number is located at index 11 


    answerFile.open(answerFilename);
}

void openStudentFile(ifstream& studentAnswers) {

    // filenames are declared as an array because 
    // ifstream class method open requires char as parameter

    char studentAnswerFilename[] = "Student Answers 1.txt";
    char studentAnswerFilename2[] = "Student Answers 2.txt";
    char studentAnswerFilename3[] = "Student Answers 3.txt";
    string userInput = "";
    while (userInput != studentAnswerFilename && userInput != studentAnswerFilename2 && userInput != studentAnswerFilename3) {
        cout << "Enter student answers filename: " << endl;
        getline(cin, userInput);
    }

    // takes from user number of file. Number is located at index 16
    studentAnswers.open(studentAnswerFilename);

}

void openOutputFile(ofstream& outputFile) {

    char outputFilename[] = "";

    cout << "Enter output filename (max 25 characters): " << endl;

    //takes input from user
    cin.getline(outputFilename, 25);
    // open file

    outputFile.open(outputFilename);
    if (!outputFile.is_open()) {
        cout << "Cant open file";
    }
}

void readAnswerKeyFile(string answerArray[], ifstream& answerFile) {
    string line;
    short i = 0;
    while (answerFile.good()) {
        getline(answerFile, line);
        answerArray[i] = line;
        i++;
    }

    answerFile.close();
}

void readStudentAnswers(string studentAnswersArray[], ifstream& studentAnswers) {
    string line;
    short i = 0;
    while (studentAnswers.good()) {
        getline(studentAnswers, line);
        studentAnswersArray[i] = line;
        i++;
    }

    studentAnswers.close();
}

int compare(string answers[], string studentAnswersArray[], bool missedQuestions[]) {
    short numberOfWrong=0;
    for (short i = 0, j = 2; i < 25, j < 27; i++, j++) {
        
        if (answers[i] != studentAnswersArray[j]) {
            missedQuestions[i] = true;
            numberOfWrong++;
            cout << answers[i];
        }
   
    }
    return numberOfWrong;
}

Part of code which is confusing is this :

if (answers[i] != studentAnswersArray[j]) {
missedQuestions[i] = true;
numberOfWrong++;
cout << answers[i];
}

I got as output only 1 element

If you want to compile make 2 text files named Answer Key 1.txt with following content:
A
B
B
D
and so on (25 items)
Next file is student Answers 1.txt with following:

id
name
A
D
C
D
(27 items)

[Salem]

> 88: char outputFilename[] = "";
This doesn't have room for 1 character, let alone 25
Use a string instead.

And when it comes to opening the file, use
outputFile.open(outputFilename.c_str());

[nedim]

I get error Unable to resolve identifier c_str

I have imported #include <cstring>

[iMalc]

You have to declare outputFilename as a std::string, as stated.

[nedim]

You have to declare outputFilename as a std::string, as stated.

I forgot to do that

After I made changes it outputs only one element instead of all

[Salem]

Can you attach examples of your two input files?

> for (short i = 0, j = 2; i < 25, j < 27; i++, j++)
The comma operator in the comparison is not doing what you seem to think it should be doing.
Perhaps you meant &&

[nedim]

Student Answers 1.txt: http://ubuntuone.com/6cIgYkTzMeFddgQjyT72bS
Answer Key 1.txt http://ubuntuone.com/7Lu89MQ92PTsH4t8xtKcQY

[rags_to_riches]

Did you bother to read Salem's post?

[nedim]

I have just tested it on windows machine and I got correct output.
It looks like my linux compiler is messed up.

[grumpy]

If code works with one compiler but not another then, about 99.999% of the time, the code is at fault, not the compiler.

No matter how much novices insist on blaming a compiler.

[Salem]

Part of the problem is your broken code to read a file - it's just a variant of how NOT to use feof().

(gdb) print i
$1 = 25
(gdb) print line
$2 = {static npos = 18446744073709551615, _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, 
    _M_p = 0x604058 ""}}
(gdb) bt
#0  0x00007ffff7b7221e in std::string::assign(std::string const&) () from /usr/lib/libstdc++.so.6
#1  0x00000000004019f5 in readAnswerKeyFile (answerArray=0x7fffffffdd70, answerFile=...) at bar.cpp:107
#2  0x00000000004013b3 in main () at bar.cpp:35

Note the value of i
It's 25, so you're off the end of your array!

Replacing both loops with
while (getline(answerFile, line))
and outputting some extra detail gives
Answer to question 5 should be A
Answer to question 6 should be A
Answer to question 7 should be A
Answer to question 24 should be B

[nedim]

Part of the problem is your broken code to read a file - it's just a variant of how NOT to use feof().

(gdb) print i
$1 = 25
(gdb) print line
$2 = {static npos = 18446744073709551615, _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, 
    _M_p = 0x604058 ""}}
(gdb) bt
#0  0x00007ffff7b7221e in std::string::assign(std::string const&) () from /usr/lib/libstdc++.so.6
#1  0x00000000004019f5 in readAnswerKeyFile (answerArray=0x7fffffffdd70, answerFile=...) at bar.cpp:107
#2  0x00000000004013b3 in main () at bar.cpp:35

Note the value of i
It's 25, so you're off the end of your array!

Replacing both loops with
while (getline(answerFile, line))
and outputting some extra detail gives
Answer to question 5 should be A
Answer to question 6 should be A
Answer to question 7 should be A
Answer to question 24 should be B

Changed both loops but it still outputs only 1 value. Even when I write to printall values it shows only one.

[nedim]

Here is my debug session: http://ubuntuone.com/0LftsYVryr3qIXUv6xxY3p

[Salem]

But if you watch carefully, you actually go into the inner loop 4 times (as mine does).

Perhaps when you print a single letter, you should also print a newline to flush the output.

            cout << "Answer to question " << i << " should be " << answers[i] << endl;

The other question, were the results I posted correct?