Use a dynamic array to sort information in C++

DynamicArrays.cpp

#include <iostream>

#include <string>

#include <fstream>

#include <iomanip>

using namespace std;

int main() {
  ifstream readFl("Ch8_Ex6Data.txt");
  string lineScan;

  int lineCounter = 0;
  int answer_key_size;
  int line_size;
  char grade = 'A';

  double percent;

  cout << "# of questions?" << endl;
  cin >> answer_key_size;
  string * answer_key = new string[answer_key_size];

  while (getline(readFl, lineScan)) //1st line(do ALL this)... 2nd line(do ALL this)... etc etc
  {

    if (lineCounter < 1) {
      cout << "Key ";
      for (int i = 0; i < lineScan.length(); i++) {
        answer_key[i] = lineScan[i];
      }

      for (int i = 0; i < answer_key_size; i++) {
        cout << answer_key[i];
      }
      cout << endl;
    }
    lineCounter++;
    if (lineCounter > 1) {
      line_size = lineScan.length();
      string * student_rows = new string[line_size]; // create dynam Arr

      //put id's and answers
      for (int i = 0; i < line_size; i++) {
        student_rows[i] = lineScan[i];
      }

      double score = 0;

      for (int i = 0; i < line_size; i++) {
        if (i > 8) {
          if (student_rows[i] == (answer_key[i - 9])) {
            score = score + 2;
          }

          if (student_rows[i] != answer_key[i - 9] && student_rows[i] != " ") {
            score = score - 1;
          }
        }
      }

      percent = (score / 40) * 100;
      if (percent >= 90) {
        grade = 'A';
      } else if (percent >= 80 && percent <= 89.99) {
        grade = 'B';
      } else if (percent >= 70 && percent <= 70.99) {
        grade = 'C';
      } else if (percent >= 60 && percent <= 69.99) {
        grade = 'D';
      } else {
        grade = 'F';
      }

      //cout indexes of dynam array
      for (int i = 0; i < line_size; i++) {
        cout << student_rows[i];
      }

      cout << " " << score << " " << grade << " " << endl;
    }
  }

  return 0;
}