Program to grade scores from a file C++

ScoreGrades.cpp

#include <iostream>

#include <string>

#include <fstream>

#include <iomanip>

using namespace std;

double score(string transferAns, string transferKey);

//MAIN FUNCTION
int main() {
  string lineScan;
  string transferKey;
  char grade = 'A';
  double cScore;
  double percent;

  int lineCounter = 0;
  ifstream readFl("Ch8_Ex6Data.txt");

  while (getline(readFl, lineScan)) {
    if (lineCounter < 1) {
      transferKey = lineScan.substr(0, 20);
    }
    lineCounter++;
    if (lineCounter > 1) {
      string transferID = lineScan.substr(0, 8);
      cout << transferID << " ";
      string transferAns = lineScan.substr(9, 29);
      cScore = score(transferAns, transferKey);
      //calculate grade via score
      percent = (cScore / 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 << cScore << " " << grade << endl;
    }
  }
  lineCounter = 0;
  return 0;
}

double score(string transferAns, string transferKey) {
  int score = 0;
  int x = 0;

  cout << transferAns <<
    " ";

  for (char c: transferAns) {
    if (c == transferKey[x]) {
      score = score + 2;
    }
    if (c != transferKey[x] && c != ' ') {
      score = score - 1;
    }
    x++; // verified correct tabulations
  }

  return score;
}