Homework [Help]

[mk7mew]

I'm still not understanding how to fix the c++ code that was asked by my prof.
She asked us to complete the entry shown below to add a function to get the student name
add function to assign a letter grade in the int main then pass to the displayResults function
ask the user if they want to use the program again with either a loop or end program

she asked not to use global variables, but use function parameters

my code is shown below on how far I got into the homework assignment. I'm still roughly new to this and everything is an online teaching right now which sometimes doesn't make sense to me, but need some help from anyone that can explain a different way if possible
it's not done obviously with my code, but I don't know if it looks right
I don't even know how I can loop this to run again for the next student I still don't understand that part

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

// 2. Function prototypes
void displayResults(string name, float avg); //satisfies the complier
int getTestScore();
float calcAvg(int t1, int t2, int t3);
bool isValid(int num, int min, int max);
char determineScore(int score);

int main()
{
    string fullName;
    int test1, test2, test3;
    float average;
    
    // get student full name
    cout << "Student Name:  ";
    getline(cin, fullName);
    
    // get 3 test scores
    test1 = getTestScore(); // function call to value returning function
    test2 = getTestScore();
    test3 = getTestScore();
    
    // average calculation
    average = calcAvg( test1, test2, test3);
    
    //assign a letter grade, using a char
    determineScore(int score, float calcAvg);
    
    //diplay heading, name and average
    displayResults(fullName, average); // function call for a void function
    
    system("pause");
    return 0;
}

    // 1. Function definiton
    // ======================================================================
    // displayResults outputs the heading and the results of the calculations
    // ======================================================================
    void displayResults(string name, float avg) // function header, scope
    {
        cout << "------------------------------------------------\n";
        cout << "Norco College \n";
        cout << " CIS-5: Intro to Programming with C++  \n";
        cout << "Student Averages \n";
        cout << "-------------------------------------------------\n";
  
        cout << name << ": " << avg << endl;
    }
        //getTestScore prompts user and gets a single test score
        int getTestScore()
        {
            int score; // scope of the operator
            int min = 0, max = 100;
            
            cout << "Enter a test score:       ";
            cin >> score;
            
            while(isValid(score, min, max)) // While score is not valid
            {
                cout << "Try again. Enter a valid test score between 0-100:   ";
            }
                
            return score; //returns a valid test score
        }

            //calcAvg totals scores and calculate the average
            float calcAvg(int t1, int t2, int t3)
            {
                float avg;
        
                avg = (t1 + t2 + t3) / 3.0;
        
                return avg;
            }
                char determineScore(int score)
                {
                  
                    char grade = 0;
                    if ( score >= 85)
                        grade = 'A' ;
                    else if (score >= 70)
                        grade = 'B' ;
                    else if (score >= 60)
                        grade = 'C' ;
                    else if( score >= 50)
                        grade= 'D';
                    else
                        grade = 'F';
                    return grade;
                }
                    
                // isValid test for valid input and returns true or false
                bool isValid(int num, int min, int max)
                {
                    if (num < min || num > max)
                        return false;
                    else
                        return true;
                }

[salem c]

Also here https://www.cplusplus.com/forum/beginner/269978/
Don't post the same thing in many places.