This is my final project for my C++ class online. I was instructed to make a test and to pull answers from withing a .txt file and compare them to the answer that the user inputs. I'm sure there's a much easier wau of doing things than the way I'm doing them, but that desn't matter to e right now. What matters to me is why I can't link my program(it compiles fine). Observe this code here:

//"Derek Elensar"
//Final Project.cpp

#include <iostream>
#include <fstream>//.h>
#include <string.h>
#include <iomanip>//.h>
#include <string.h>
#include <stdio.h>
#include <cstdlib>

/*
using std::cin;
using std::cout;
using std::endl;
using std::string;
using std::ios;
using std::fstream;
using std::fixed;
*/
using namespace std;

double check_answer(char user_answer[2], char answer_from_file[2] , double);
char check_case(char user_answer[2]);

int main()
{
    double percentage;
    const int points_possible = 20;
    fstream answers_in;
    char user_answer[2];
    char answer_from_file[2];
    double tempscore;
    fstream score_out;
    char firstname[16], lastname[16];

    cout << "What is your first name?\n>";
    cin.get(firstname, 16);
    cin.ignore(80, '\n');

    cout << "What is your last name?\n>";
    cin.get(lastname, 16);
    cin.ignore(80, '\n');


    strcat(firstname, " ");
    strcat(firstname, lastname);
    strcat(firstname, ".TXT");


    answers_in.open("ANSWERS.TXT", ios::in);
    score_out.open(firstname, ios::out);

    if(!answers_in)
    {
        cout << "ERROR: Could not open answers.txt!\n";
        return 0;
    }
    if(!score_out)
    {
        cout << "ERROR: Could not output score file!\n";
        return 0;
    }
    else
    {
        system("CLS");
        //1
        cout << "choose A\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");

        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //2
        cout << "choose B\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //3
        cout << "choose C\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //4
        cout << "choose D\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //5
        cout << "choose A\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //6
        cout << "choose B\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //7
        cout << "choose C\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //8
        cout << "choose D\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //9
        cout << "choose A\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //10
        cout << "choose B\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //11
        cout << "choose C\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //12
        cout << "choose D\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //13
        cout << "choose A\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //14
        cout << "choose B\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //15
        cout << "choose C\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //16
        cout << "choose D\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //17
        cout << "choose A\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);
        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //18
        cout << "choose B\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);
        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //19
        cout << "choose C\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);

        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //20
        cout << "choose D\n"
             << "A) answer\tB) answer\n"
             << "C) answer\tD) answer\n";
        cin.get(user_answer, 2);
        cin.ignore(80, '\n');
        user_answer[0] == check_case(user_answer);
        answers_in >> answer_from_file;

        system("CLS");


        tempscore = check_answer(user_answer, answer_from_file, tempscore);

        //================================================
        percentage = (tempscore / points_possible) * 100;
        cout << "You got " << tempscore << '/' << points_possible
             << " meaning that\n Your score was a " << percentage << "%\n";
    }
    answers_in.close();
    score_out << percentage << "%\n";
    score_out.close();
    return 0;
}


double check(char user_answer[2], char answer_from_file[2], double tempscore)
{
    if(strcmp(user_answer, answer_from_file) == 0)
        {
            tempscore++;
            //cout << tempscore << endl;
        }
        return tempscore;
}

char check_case(char user_answer[2])
{
    if(user_answer[0] == 'a' || user_answer[0] == 'b' || user_answer[0] == 'c' || user_answer[0] == 'd'){
            user_answer[0] -= 32;}
    return user_answer[0];
}

now when I compile, I get these errors:

undefined reference to `check_answer(char*, char*, double)'|
undefined reference to `check_answer(char*, char*, double)'|
undefined reference to `check_answer(char*, char*, double)'|
undefined reference to `check_answer(char*, char*, double)'|
undefined reference to `check_answer(char*, char*, double)'|
more undefined references to `check_answer(char*, char*, double)' follow|
||=== Build finished: 6 errors, 0 warnings ===|

It doesn't give me any line numbers or anything, and I'm quite baffled at my sityation... If someone could help me with this, I would greatly appreciate it.

DISCLAIMER: this IS homework, and I'm not asking for you to do it for me.. as you can see, I have it pretty much all done(except for actually putting the questions in there meself.. I gotta think about what I wanna ask :P )I am merely asking for help with the errors that I'm getting.

Thanks,
Derek Elensar
:)

Your final project does not include C++ classes, inheritance and all that fun stuff? Thats a weird programming/C++ class!

Yeah... you're telling me... sucky class.. pretty much worthless teacher who, when you asked for help, either gave you unclear information or gave you the answer to your problem... noth of those solutions are pretty much not that good for anyone.. :P

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