I am getting unknown ascii code characters in my program console output

Question

My program basically ask user for inputs and it saves data like login data, username in a text file and uses same file to retrieve data and displays in the output console. When program executes users can choose between options 1 to 6, option 6 is for existing out of the application and rest of the options from 1 to 5 are for users to input data and to view stored data in the file.

When program displays data in the console, I see lots of unnecessary ASCii code. Why is it showing up and how do I make them go ? Thanks!!

int main() {
    //Considering the max length of data entered (name) to be 15.
    char data[15];
    int n = 0, option = 0, count_n = 0;
    //This is the initial mark alloted to a subject.
    string empty = "00";
    string proctor = "";
    //Name of the file in which DB is stored.
    ifstream f("Example.txt");
    string line;

    //The following for loop counts the total number of lines in the file.
    for (int i = 0; std::getline(f, line); ++i) {
        count_n++;
    }

    while (option != 6) {
        //This prints out all the available options in the DB
        cout << "\nAvailable operations: \n1. Add New Students\n2."
            << "Student Login\n3. Faculty Login\n4. Proctor Login\n5. Admin View\n"
            << "6. Exit\nEnter option: ";
        cin >> option;

        if (option == 1) {
            cout << "Enter the number of students: ";
            cin >> n;

            count_n = count_n + n;

            for (int i = 0; i < n; i++) {
                ofstream outfile;
                outfile.open("Example.txt", ios::app);
                //The entire data of a single student is stored line-by-line.
                cout << "Enter your registration number: ";
                cin >> data;
                outfile << data << "\t";

                cout << "Enter your name: ";
                cin >> data;
                int len = strlen(data);

                while (len < 15) {
                    data[len] = ' ';
                    len = len + 1;
                }
                outfile << data << "\t";
                //Inserting empty data initially into the file
                outfile << empty << "\t";
                outfile << empty << "\t";
                cout << "\b \b";

                cout << "Enter your proctor ID: ";
                cin >> proctor;

                outfile << proctor << endl;

            }
        }

        else if (option == 2) {
            char regno[9];
            cout << "Enter your registration number: ";
            cin >> regno;
            ifstream infile;
            int check = 0;
            infile.open("Example.txt", ios::in);

            //This loop prints out the data according to the registration number specified.
            while (infile >> data) {
                if (strcmp(data, regno) == 0) {
                    cout << "\nRegistration Number: " << data << endl;
                    infile >> data;
                    cout << "Name: " << data << endl;

                    infile >> data;
                    cout << "CSE1001 mark: " << data << endl;

                    infile >> data;
                    cout << "CSE1002 mark: " << data << endl;

                    infile >> data;
                    cout << "Proctor ID: " << data << endl;

                    infile.close();
                    check = 1;
                }
            }

            if (check == 0) {
                cout << "No such registration number found!" << endl;
            }

        }

        //This loop is used to view and add marks to the database of a student.
        else if (option == 3) {
            char subcode[7];
            cout << "Enter your subject code: ";
            cin >> subcode;
            string code1 = "CSE1001", code2 = "CSE1002", mark = "";
            ifstream infile;
            int check = 0;

            cout << "\nAvailable operations: \n1. Add data about marks\n"
                << "2. View data\nEnter option: ";
            cin >> option;

            if (option == 1) {
                cout << "Warning! You would need to add mark"
                    << "details for all the students!" << endl;
                for (int i = 0; i < count_n; i++) {
                    fstream file("Example.txt");

                    //The seek in file has been done according to the length
                    //of the data being inserted. It needs to adjusted accordingly
                    //for diffferent lengths of data.

                    if (strcmp(subcode, code1.c_str()) == 0) {
                        file.seekp(26 + 37 * i, std::ios_base::beg);
                        cout << "Enter the mark of student#" << (i + 1) << " : ";
                        cin >> mark;
                        file.write(mark.c_str(), 2);
                    }

                    if (strcmp(subcode, code2.c_str()) == 0) {
                        file.seekp(29 + 37 * i, std::ios_base::beg);
                        cout << "Enter the mark of student#" << (i + 1) << " : ";
                        cin >> mark;
                        file.write(mark.c_str(), 2);

                    }
                }

            }

            //This loop is used to view marks of a student.
            //The extra infile commands have been used to get a specific mark 
            //only since the data has been seperated by a tabspace.

            else if (option == 2) {
                infile.open("Example.txt", ios::in);
                if (strcmp(subcode, code1.c_str()) == 0) {
                    cout << "Registration number - Marks\n" << endl;
                    while (infile >> data) {
                        cout << data;
                        infile >> data;
                        infile >> data;
                        cout << " - " << data << endl;
                        infile >> data;
                        infile >> data;
                        check = 1;
                    }
                }

                infile.close();
                infile.open("Example.txt", ios::in);

                if (strcmp(subcode, code2.c_str()) == 0) {
                    cout << "Registration number - Marks\n" << endl;
                    while (infile >> data) {
                        cout << data;
                        infile >> data;
                        infile >> data;
                        infile >> data;
                        cout << " - " << data << endl;
                        infile >> data;
                        check = 1;

                    }
                }
            }

            infile.close();

            if (check == 0) {
                cout << "No such subject code found!" << endl;
            }

        }

        //This loop displays all the details of students under the same proctor ID. 

        else if (option == 4) {
            char procid[7];
            cout << "Enter your proctor ID: ";
            cin >> procid;
            int check = 1;
            char temp1[100], temp2[100], temp3[100];
            char temp4[100], id[100];
            ifstream infile;
            infile.open("Example.txt", ios::in);

            while (infile >> temp1) {
                infile >> temp2;
                infile >> temp3;
                infile >> temp4;
                infile >> id;

                if (strcmp(id, procid) == 0) {
                    cout << "\nRegistration Number: " << temp1 << endl;
                    cout << "Name: " << temp2 << endl;
                    cout << "CSE1001 Mark: " << temp3 << endl;
                    cout << "CSE1002 Mark: " << temp4 << endl;
                    check = 1;
                }
            }

            if (check == 0) {
                cout << "No such proctor ID found!" << endl;
            }
        }

        //This loop acts as an admin view to see all the data in the file.

        else if (option == 5) {
            char password[25];
            cout << "Enter the admin password: ";
            cin >> password;

            //This variable value can be changed according to your requirement 
            //of the administrator password.

            string admin_pass = "admin";

            if (strcmp(password, admin_pass.c_str()) == 0) {
                cout << "Reg No.     \tName\tCSE1001\tCSE1002\tProctor ID" << endl;
                ifstream infile;
                infile.open("Example.txt", ios::in);
                char data[20];

                while (infile >> data) {
                    cout << data << "\t";
                    infile >> data;
                    cout << data << "\t";
                    infile >> data;
                    cout << data << "\t";
                    infile >> data;
                    cout << data << "\t";
                    infile >> data;
                    cout << data << endl;

                }
            }
        }
    }
}

Here is the output:

Answer 1

The ╠ character is a box drawing character. In code page 437 it is represented by hex value 0xCC.

In this case it is a magic hex value that means it is uninitialised stack memory.

The data array is 20 characters long, but it degrades into a pointer and the operator<< outputs characters until it gets a null character. So in this case lots of uninitialized memory ╠ characters until a \0 character is found in memory.

---

It seems that the uninitialized data variable was written to the file on a previous run and now it is read back as-is. If the read was unsuccessful it would probably have placed a \0 in the first position of the data char array and there would have been no output in that case.

I ran the program with an empty input file and added a single student. This was stored in the text file (viewed with Visual Studio's text editor):

REGNUM123   Pete           ÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌ    00  00  PROC432

In this case Ì, or latin capital letter i with grave character is the 0xCC hex value in Unicode and multiple other encodings. When adding the student the number of characters written does not necessarily equal the number of characters in the data array (15 in that case). They are written until a \0 is found.

Answer 2

Most probably you have multiple buffer overruns:

        char password[25];
        cout << "Enter the admin password: ";
        cin >> password;

If someone inputs more than 24 bytes (characters) as a password, you will have buffer overrun of password. You should do it this way:

        std::string password;
        cout << "Enter the admin password: ";
        cin >> password;

The same thing is valid for output, you're potentially buffer overrunning char data[20];. Furthermore, you can't use infile >> data like that for reading from file. You have to use infile.getline():

int col_count = 4;

while (true) {
    infile.getline(data, 20);  // 20 is the size of the buffer.
    if(infile.good()) {
        cout << data;
        if(--col_count == 0) {
            col_count = 4;
            cout << '\n';
        }
        else cout << '\t';
    }
    else break;
}