Grade school : ARM64 - Some tests fail when run online about c HOT 5 CLOSED

#ifndef GRADE_SCHOOL_H
#define GRADE_SCHOOL_H

#include <stddef.h>
#include <stdint.h>
#include <stdbool.h>

#define MAX_NAME_LENGTH 20
#define MAX_STUDENTS 20

typedef struct {
    uint8_t grade;
    char    name[MAX_NAME_LENGTH];
} student_t;

typedef struct {
    size_t    count;
    student_t students[MAX_STUDENTS];
} roster_t;

int name_comparator(const void* first, const void* second);
int grade_comparator(const void* first, const void* second);

void     init_roster(roster_t* roster);
bool     add_student(roster_t* roster, char* name, int grade);
roster_t get_grade(roster_t* roster, uint8_t desired_grade);

#endif

#include <string.h>
#include <stdlib.h>
#include <stdio.h>

#include "grade_school.h"

roster_t result;
void     print_roster(roster_t* roster);
void     print_roster(roster_t* roster) {
    size_t i = 0;
    for (i = 0; i < roster->count; i++) {
        printf("[%-20s] %2d\n", roster->students[i].name, roster->students[i].grade);
    }
    printf("-------------\n");
}

int name_comparator(const void* first, const void* second) {
    student_t* s1 = (student_t*)first;
    student_t* s2 = (student_t*)second;
    return strncmp(s1->name, s2->name, MAX_NAME_LENGTH);
}

int grade_comparator(const void* first, const void* second) {
    student_t* s1 = (student_t*)first;
    student_t* s2 = (student_t*)second;
    return s1->grade - s2->grade;
}

void init_roster(roster_t* roster) {
    memset((void*)roster, 0, sizeof(roster_t));
}

bool add_student(roster_t* roster, char* name, int grade) {
    size_t i = 0;
    for (i = 0; i < roster->count; i++) {
        if (strncmp(roster->students[i].name, name, MAX_NAME_LENGTH) == 0)
            return false;  // forbid adding student twice
    }

    i = 0;
    while (roster->students[i].grade != 0) {
        i++;
        if (i == MAX_STUDENTS)
            return false;
    }
    roster->students[i].grade = grade;
    strncpy(roster->students[i].name, name, MAX_NAME_LENGTH);
    roster->count++;

    qsort((void*)roster->students, roster->count, sizeof(student_t), name_comparator);
    qsort((void*)roster->students, roster->count, sizeof(student_t), grade_comparator);
    print_roster(roster);
    return true;
}

roster_t get_grade(roster_t* roster, uint8_t desired_grade) {
    result.count = 0;
    for (size_t i = 0; i < roster->count; i++) {
        if (roster->students[i].grade == desired_grade) {
            memcpy((void*)&result.students[result.count], (void*)&roster->students[i], sizeof(student_t));
            result.count++;
        }
    }
    return result;
}