I need help with grading tests C++ project

Each line represents the four tests taken by students in a class during the semester.  You need to calculate the average for each student in the class by reading in the file.  Display the average for each student, a space, and with their letter grade.

44 55 77 88
79 88 100 99
77 99 98 99
100 88 89 100
55 56 40 77
100 100 99 95
88 84 87 88
96 97 99 100
30 44 77 55
79 77 88 0
54 52 60 77
88 77 88 77
44 77 10 95

#include <iostream>
#include <string>
#include <fstream>
using namespace std;


double calculateAvg(int studentNum)
{
fstream infile("grades.txt",ios::in);
if(!infile){cout<<"file could not be found!";exit(1);}

double sum = 0; //sum of all test scores
double testScore; //individual student test score
int i = 0;

 while( i < 4 ) {
      infile >> testScore;
 sum = sum + testScore;
      i++;
   }

 infile.close();

return sum/4.0;
 

}

void printGrade(double average)
{
if (average >= 90)
cout << "A" << endl;
 else if (average >= 80)
cout << "B" << endl;
 else if (average >= 70)
cout << "C" << endl;
else if (average >= 60)
cout << "D" << endl;
else
cout << "F" << endl;
}

int main()
{
const int NUM_OF_STUDENTS = 0;
double averages[NUM_OF_STUDENTS];
//calculates and stores 10 students averages
int i = 0;

while(i<NUM_OF_STUDENTS) {
    averages[i] = calculateAvg(i);
      i++;
       
   }
  cout<<(averages[i])<<" ";
printGrade(averages[i]);
}