Use arrays to re arrange scores highest to lowest in C++

ReArrangeScores.cpp

#include <iostream>

#include <string>

#include <fstream>

#include <iomanip>

#include <sstream>

using namespace std;

struct studentType {
  string studentFname;
  string studentLname;
  int testScore;
  char grade;
}
sU;

void buildObject(
  struct studentType stud[20],
  string lastName,
  string firstName,
  string score,
  int plus1,
  studentType & studentFname,
  studentType & studentLname,
  studentType & testScore,
  studentType & grade
);

void sortObject(
  struct studentType stud[20],
  string tmpFnA,
  string tmpFnB,
  string tmpLnA,
  string tmpLnB,
  int tmpTstA,
  int tmpTstB,
  char tmpGrdA,
  char tmpGrdB
);

void gradeObject(
  struct studentType stud[20]
);

void printObject(
  struct studentType stud[20]
);

int main() {
  ifstream inData;
  inData.open("Ch9_Ex2Data.txt");
  ofstream outData;
  outData.open("Ch9_Ex2Out.txt");
  struct studentType stud[20];
  int plus1 = 0;
  string lastName, firstName, score,
  tmpFnA, tmpLnA,
  tmpFnB, tmpLnB;
  int tmpTstA, tmpTstB;
  char tmpGrdA, tmpGrdB;
  studentType fName, lName, tScore, gD;

  buildObject(
    stud, lastName, firstName, score, plus1,
    fName, lName, tScore, gD
  );

  sortObject(
    stud, tmpFnA, tmpFnB, tmpLnA,
    tmpLnB, tmpTstA, tmpTstB, tmpGrdA,
    tmpGrdB
  );

  gradeObject(
    stud
  );

  //print object
  printObject(
    stud
  );

  inData.close();
  outData.close();

  return 0;
}

//"A function to read the students’ data into the array."
void buildObject(
  struct studentType stud[20],
  string lastName,
  string firstName,
  string score,
  int plus1,
  studentType & studentFname,
  studentType & studentLname,
  studentType & testScore,
  studentType & grade
) {
  ifstream inData;
  inData.open("Ch9_Ex2Data.txt");
  while (inData >> lastName >> firstName >> score) {
    stud[plus1].studentFname = firstName;
    stud[plus1].studentLname = lastName;
    stud[plus1].testScore = stoi(score);
    stud[plus1].grade = 'F';
    plus1++;
  }
}

//"A function to print the names of the students having the highest test score."
void sortObject(
  struct studentType stud[20],
  string tmpFnA,
  string tmpFnB,
  string tmpLnA,
  string tmpLnB,
  int tmpTstA,
  int tmpTstB,
  char tmpGrdA,
  char tmpGrdB
) {
  for (int a = 0; a < 20; a++) {
    for (int b = a; b < 20; b++) {
      if (stud[b].testScore > stud[a].testScore) {
        tmpFnA = stud[a].studentFname;
        tmpLnA = stud[a].studentLname;
        tmpTstA = stud[a].testScore;
        tmpGrdA = stud[a].grade;
        tmpFnB = stud[b].studentFname;
        tmpLnB = stud[b].studentLname;
        tmpTstB = stud[b].testScore;
        tmpGrdB = stud[b].grade;
        stud[a].studentFname = tmpFnB;
        stud[a].studentLname = tmpLnB;
        stud[a].testScore = tmpTstB;
        stud[a].grade = tmpGrdB;
        stud[b].studentFname = tmpFnA;
        stud[b].studentLname = tmpLnA;
        stud[b].testScore = tmpTstA;
        stud[b].grade = tmpGrdA;
      }
    }
  }
}

//"A function to assign the relevant grade to each student."
void gradeObject(struct studentType stud[20]) {
  for (int i = 0; i < 20; i++) {
    if (stud[i].testScore >= 90) {
      stud[i].grade = 'A';
    } else if (stud[i].testScore >= 80 && stud[i].testScore <= 89) {
      stud[i].grade = 'B';
    } else if (stud[i].testScore >= 70 && stud[i].testScore <= 79) {
      stud[i].grade = 'C';
    } else if (stud[i].testScore >= 60 && stud[i].testScore <= 69) {
      stud[i].grade = 'D';
    } else {
      stud[i].grade = 'F';
    }
  }
}

//"A function to print the names of the students having the highest test score."
void printObject(struct studentType stud[20]) {
  ofstream outData;
  outData.open("Ch9_Ex2Out.txt");
  for (int i = 0; i < 20; i++) {
    cout << stud[i].studentFname << ", " << stud[i].studentLname << " " << stud[i].testScore << " " << stud[i].grade << endl;
    outData << stud[i].studentFname << ", " << stud[i].studentLname << " " << stud[i].testScore << " " << stud[i].grade << endl;
  }
}