Store Input from Text File into Arrays or Variables? - c++

Question

My Problem:
I am very new to new to programming and trying to write a program in C++, I have a text file. *In the text file is stored is a Students Name, Grade, and Grade Letter. I want them stored as different types in arrays *
I want to store them individually in an array....
ie text file would look like this:
Jill Hamming A 96
Steven Jenning A 94
Tim Sutton B 89
Dillon Crass C 76
Sammy Salsa D 54
Karen Poulk D 49
I would like to store all the First names in one array, last names in another etc. So on and so on.
These arrays will later be assigned to object for the student. There maybe up to 500 students.
So the question:
How to store input from a text document into an array instead of using 500 variables.
ie. Here is my attempt.
int main()
{
/// the input is all different types, strings, ints and chars
string my_First_Name[500], my_Last_Name[500];
int my_grade[500];
char my_letter[500];
ifstream myfile("input.txt");
if (myfile.is_open()){
for (int i = 0; i < 500; i++) {
myfile >> my_First_Name[i] >> my_Last_Name[i] >> my_grade[i] >> my_letter[i];
}
// much later and irrelevent part but just showing because this is what I want to do. where Student Class exsists somewhere else. yet to be programmed.
Student myStudent [500];
myStudent[i].Grades = my_grade[i];
myStudent[i].LetterGrade = my_letter[i];
}
myfile.close();
//Exit
system("pause");
return 0;
}
When I went to print out what I had. I had all negative and weird numbers which means it was not initialized. Where did I go wrong?

Answer 1

When you have multiple arrays of the same size, it is usually as sign of poor design.
The rule of thumb is to have a record (or line of data) represented by a class or structure:
struct Record
{
string first_name;
string last_name;
int grade_value; // Can this go negative?
string grade_text;
};
If you know you are going to have 500, you can create an array for the data:
#define ARRAY_CAPACITY (500)
Record grades[ARRAY_CAPACITY];
This not a great solution, because you waste space if there are less than 500 and perform buffer overrun if you read more than 500.
Thus a better solution is to use std::vector, which allows you to append records as you read them. The std::vector will expand as necessary to contain the records. With an array, you would have to allocate a new array, copy old records to new array, then delete the old array.
Also, a good solution will include methods, inside Record, to read the data members from an input stream. Research "overloading stream extraction operator".
You input loop should look something like:
Record r;
while (input_file >> r)
{
student_grades.push_back(r);
}
You can find this information by searching stackoverflow. A good beginning search is "stackoverflow c++ read file space separated" or "comma separated" or "stackoverflow c++ read file structure".
Reading a record
You could expand the loop to something like this:
std::vector<Record> student_grades;
Record r;
while (input >> r.first_name >> r.last_name >> r.grade_value >> r.grade_text)
{
student_grades.push_back(r);
}
If you are allergic or limited to arrays, you will need to use a counter with the array.
#define MAXIMUM_RECORDS (500)
Record r;
Record grade_book[MAXIMUM_RECORDS];
unsigned int record_count = 0U;
while (input >> r.first_name >> r.last_name >> r.grade_value >> r.grade_text)
{
grade_book[record_count] = r;
++record_count;
if (record_count >= MAXIMUM_RECORDS)
{
break;
}
}
A for loop is not used because we don't know how many records are in the file, only a maximum that the program will read. If the file has 600 records, only 500 will be read.