Create an array with external file in C++ - c++

Question

I have 4 days of training in C++, so bear with me.
Two data files are required to evaluate a multiple-choice examination. The first file
(booklet.dat) contains the correct answers. The total number of questions is 50. A sample
file is given below:
ACBAADDBCBDDAACDBACCABDCABCCBDDABCACABABABCBDBAABD
The second file (answer.dat) contains the students’ answers. Each line has one student
record that contains the following information:
The student’s answers (a total of 50 answers) in the same format as above (* indicates no answer)., followed by Student ID and Student Name. Example:
AACCBDBC*DBCBDAAABDBCBDBAA*BCBDD*BABDBCDAABDCBDBDA 6555 MAHMUT
CBBDBC*BDBDBDBABABABBBBBABBABBBBD*BBBCBBDBABBBDC** 6448 SINAN
ACB*ADDBCBDDAACDBACCABDCABCCBDDABCACABABABCBDBAABD 6559 CAGIL
I have a homework assignment to write a C++ program that counts the total number of correct answers by each student and outputs this information to another file called report.dat. In this file, the student’s IDs, names and scores must be given. Each correct answer is worth 1 point. For the sample files given above, the output should be as follows:
6555 MAHMUT 10
6448 SINAN 12
6550 CAGIL 49
Here's what I have so far:
include <iostream>
include <fstream>
using namespace std;
int main()
{
char booklet[50] answers[50]
int counter
// Link answers with booklet.dat
booklet = ifstream
input_file("booklet.dat");
return 0;
// Link answers with answers.dat
answers = ifstream
input_file("answer.dat");
return 0;
while (booklet==answers)
{
counter++
cout << "The student had">>counter>> "answers right";
}
}
I'm not even sure I am in the correct direction. I know I need to create an array from the file booklet.dat and another one from the file answer.dat. Then the comparison has to be made and the matches between the two have to be counted.
I don't expect anyone to do the assignment for me, i just need a nudge in the right direction.

Answer 1

1.) On your Syntax:
a) Each line in C++ has to end with an ";". There are some lines in your excample which don't. (Normally your compile should point at this or the following line with an error)
b) Multiple variable definitions need a "," in between two different variables.
2.) I would recommend you to use something like that:
(have a look at C++ Reference fstream)
EDIT: just a little outline, which is not complete in this form, just to give you and idea ;-)
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
int main()
{
int nr_of_students = 1000; /* Or any number you'd like to analyze */
int stud_nr[nr_of_students];
string stud_name[nr_of_students];
int stud_count[nr_of_students];
fstream in_out;
in_out.open("filename.dat",fstream::in); // fstream::in for reading from file
// fstream::out for writing to this file
if(in_out.is_open())
{
for(lines=0;(in_out>>answers && lines<nr_of_students);lines++)
{
in_out >> stud_nr[lines]; /* EDIT: sorry hat some index confusions here... */
in_out >> stud_name[lines];
stud_count[lines]=0;
for(int i=0;i<50;i++)
{
/* comparison between the booklet_array and the answers_array */
/* Count up the stud_count[lines] for each right comparison */
}
}
/* some simmilar code for the output-file */
}
else cout << "Error reading " << "filename.dat" << endl;
return 1;
}
3.) Your code would also get more performance with vectors.
A good Tutorial would be: Tutorial part I
and you find part 2 in the comments there
4.) you can achieve a more dynamic code with argc and argv**, just google for that
I hope these comments help you a little bit to carry on ;)

Answer 2

You are already on the right direction. Basically you want to load the answer key into an array for fast comparison and then you need to check the answers of each student and each time they get a correct answer you increment a counter and write the ID, name and score for each student. There are problems with your code such as missing semicolons.
Also please note that returning exits a function and that no statements after an unconditional return are executed, returning from main terminates your program.
The normal approach to open a file for reading is:
#include<fstream>
#include<string>
int main()
{
std::ifstream input_file("inputfilename");
// since the answer key is one line
// and each students answer , id and name are also one line
// getting that line using std::getline() would be sufficient
std::string line;
std::getline(input_file, line);
// line would now contain the entire first line except the newline character
std::getline(input_file, line);
//now line would now contain the second line in the file
return 0;
}
Writing to a file is similar we use ofstream to open a file for writing.
Like so:
#include<fstream>
int main()
{
std::ofstream output_file("outputfilename");
// lets say we have a string and an int that we want to write
std::string line_to_write("Hello File");
int number = 42;
output_file << line_to_write << number; // writes the string and then 42 on the same line
output_file << '\n'; // writes the newline character so that next writes would appear on another line
return 0;
}
For references to the standard library and C++ in general when you need to know the available functions to do something I recommend cppreference here are the specific pages on ifstream and ofstream.