Linked List (Adlaon/Amalin)

#include <iostream>
#include <string>

using namespace std;

struct Node
{
    string name;
    int grade;
    Node *next;
};

void append(Node **head_ref, string new_name, int new_grade);
void equalGrade(Node *node, int grade);
void greaterThanGrade(Node *node, int grade);
void lessThanGrade(Node *node, int grade);
void printList(Node *node);

int main()
{
    Node *head = NULL;
    string name = " ";
    int grade = 0;
    bool valid = false;
    char entry = ' ';
    bool quit = false;
    char choice = ' ';
    int gradeCheck = 0;

    while(!quit)
    {
        cout << "Enter name: ";
        getline(cin, name);

        valid = false;
        while(!valid)
        {
            cout << "Enter grade: ";
            cin >> grade;
            if(cin.good() && grade > 0) valid = true;
            else
            {
                cout << "Invalid grade!" << endl;
                cin.clear();
                cin.ignore();
            }
        }
        append(&head, name, grade);

        valid = false;
        while(!valid)
        {
            cout << "Another entry(Y/N)? ";
            cin >> entry;
            if(toupper(entry) == 'N')
            {
                valid = true;
                quit = true;
            }
            else if (toupper(entry) == 'Y')
            {
                valid = true;
                cin.clear();
                cin.ignore();
            }
            else
            {
                cin.clear();
                cin.ignore();
            }
            cout << "\n";
        }
    }

    while(true)
    {
        cout << "Criteria for displaying the list:\n";
        cout << "A. Grade =\n";
        cout << "B. Grade >\n";
        cout << "C. Grade <\n";
        cout << "D. All\n";

        valid = false;
        while(!valid)
        {
            cout << "Enter choice(A-D): ";
            cin >> choice;

            if(toupper(choice) == 'A' || toupper(choice) == 'B' || toupper(choice) == 'C')
            {
                valid = false;
                while(!valid)
                {
                    cout << "Enter grade: ";
                    cin >> gradeCheck;
                    if(cin.good() && gradeCheck > 0)
                    {
                        cout << "\n";
                        valid = true;
                    }
                    else
                    {
                        cout << "Invalid grade!" << endl;
                        cin.clear();
                        cin.ignore();
                    }
                }
            }
            else if(toupper(choice) == 'D') valid = true;
            else
            {
                cin.clear();
                cin.ignore();
            }
        }

        switch(toupper(choice))
        {
            case 'A':
                equalGrade(head, gradeCheck);
                break;

            case 'B':
                greaterThanGrade(head, gradeCheck);
                break;

            case 'C':
                lessThanGrade(head, gradeCheck);
                break;

            case 'D':
                printList(head);
                break;

            default:
                cout << "Invalid input!\n";
        }
    }

    return 0;
}

void append(Node **head_ref, string new_name, int new_grade)
{
    Node *new_node = new Node();
    Node *last = *head_ref;

    new_node->name = new_name;
    new_node->grade = new_grade;

    new_node->next = NULL;

    if(*head_ref == NULL)
    {
        *head_ref = new_node;
        return;
    }

    while(last->next != NULL) last = last->next;

    last->next = new_node;
    return;
}

void equalGrade(Node *node, int grade)
{
    while(node != NULL)
    {
        if(grade == node->grade)
        {
            cout << "Name: " << node->name << endl;
            cout << "Grade: " << node->grade << endl;
            cout << "\n";
        }
        node = node->next;
    }
}

void greaterThanGrade(Node *node, int grade)
{
    while(node != NULL)
    {
        if(grade < node->grade)
        {
            cout << "Name: " << node->name << endl;
            cout << "Grade: " << node->grade << endl;
            cout << "\n";
        }
        node = node->next;
    }
}

void lessThanGrade(Node *node, int grade)
{
    while(node != NULL)
    {
        if(grade > node->grade)
        {
            cout << "Name: " << node->name << endl;
            cout << "Grade: " << node->grade << endl;
            cout << "\n";
        }
        node = node->next;
    }
}

void printList(Node *node)
{
    while(node != NULL)
    {
        cout << "Name: " << node->name << endl;
        cout << "Grade: " << node->grade << endl;
        cout << "\n";
        node = node->next;
    }
}