exploit the vulnerability of a program to get code (in C)

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

char secret_message[8];

#define MAX_USERS 4
#define NAME_SIZE 8
struct Name {
char name[NAME_SIZE];
};
struct NameList {
unsigned long int user_num;
struct Name users[MAX_USERS];
};

void view_user(char* data) {
// this function's source code is irrelevant to the task requirements
// it does pretty output of the data in a name
}

void generate_random_string(char *dest, size_t length) {
// this function's source code is irrelevant to the task requirements
}

void input_name(char* dest) {
// this function's source code is irrelevant to the task requirements
// it takes user input and put it into a destination
}

int entry(int is_admin) {
unsigned int index;
int choice;
struct NameList NameList;
NameList.user_num = 0;
for (int i = 0; i < MAX_USERS; i++) {
memset(NameList.users[i].name, 0, NAME_SIZE);
}


if (is_admin != 0) {
    generate_random_string(secret_message, 8);
    printf("\nDear admin, here are the secret message for you %s\n", secret_message);
} 

while (1) {
    printf("======== COMP3355's StudentList =========\n");

    printf("1. Add\n");
    printf("2. View\n");
    printf("3. Delete\n");
    printf("4. Refresh\n");
    printf("5. Exit\n");
    printf("------ Used Pages: %- 11lu -------\n", NameList.user_num);

    printf("--------------------------------------\n");
    printf("Choose an option: ");
    scanf("%d", &choice);
    getchar();
    fflush(stdin);

    switch (choice) {

        case 1:
            input_name(NameList.users[NameList.user_num].name);

            printf("Added:\n");
            view_user(NameList.users[NameList.user_num].name);
            
            NameList.user_num++;
            break;

        case 2:
            printf("Enter an index to view: ");
            scanf("%d", &index);
            
            if (index >= NameList.user_num || index < 0) {
                printf("Invalid index!\n");
                return;
            }

            view_user(&NameList.users[index].name);
            break;

        case 3:
            printf("Enter an index to delete: ");
            scanf("%d", &index);
            
            if (index > NameList.user_num || index < 0) {
                printf("Invalid index!\n");
                return;
            }

            int a = NameList.user_num - 1;
            for (int i = index; i < a; i++) {
                NameList.users[i] = NameList.users[i + 1];
            }
            
            NameList.user_num--;
            printf("Deleted!\n");
            break;

        case 4:
            return 1;

        case 5:
            return 0;

        default:
            printf("Invalid choice!\n");
    }
    printf("\n");

}
}

int main() {
long int is_admin = 0;
char input_password[16];
char admin_password[16];




memset(&input_password, 0, 16);
generate_random_string(admin_password, 15);

printf("\nThis is COMP3355's student list\n");
printf("\nEnter your password: ");
scanf("%16s", input_password);

if (strncmp(input_password, admin_password, 15) == 0) {
    is_admin = 1;
}

while (1) {
    if (entry(is_admin) == 0) {
        break;
    }
}

return 0;
}

given the above C-program
You can add, read, delete usernames, clear and refresh the whole name list, or exit the program by typing the option number (1~5):
n In the computer’s memory, characters (‘ABCD…’) are stored as corresponding numbers (in hex, A: 41, B: 42, …).
n Our user list takes hex numbers in one line without spaces as inputs when adding users, and outputs both the hex number and their characters, but some characters are unprintable.
n The program also properly handled the endianness, you can directly type hex numbers and check what is shown. To know more, search about “ASCII code”and “endianness”.
When starting the application, it asks you to input a password, if you input the correct password, you can enter the admin mode to get a secret. But the password is randomly generated every time, which you will never know.

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