Vector on C

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

// Data model
typedef struct {
    struct student *next;
    int id;
    char name[20];
    int age;
} student;

// Smth like constructor
student frst = {NULL, -1, "_SERVICE_ELEM", 0};
student *first = &frst, *last = &frst;

// Free memory recursively
void cleanup(student *start)
{
    if (start->next != NULL) {
        cleanup(start->next);
    }
    printf("Cleaned id: %d name: %s\n", start->id, start->name);
    free(start);
    start = NULL;
}

// Data output
void print()
{
    student *ptr = first->next;
    printf("\nList of students:\n");

    while (ptr != NULL)
    {
        printf("%d Student %s is %d years old\n", ptr->id, ptr->name, ptr->age);
        ptr = ptr->next;
    }
}

// Generate new data element
void add(const char *name, const int age)
{
    last->next = (student *)malloc(sizeof(student));
    ((student *)(last->next))->id = last->id + 1;

    last = last->next;

    last->next = NULL;
    strcpy(last->name, name);
    last->age = age;
}

// Add new student
void new_student()
{
    char name[20] = { 0 };
    int age = 0;

    printf("Enter the student name: ");
    scanf("%19s", name);
    printf("Enter the student age: ");
    scanf("%d", &age);

    add(name, age);
}

// Start
int main()
{
    while (1)
    {
        printf("Add new student?(yes/no): ");
        char str[4]; scanf("%3s", str);

        if (!strcmp(str, "no") || !strcmp(str, "n")) {
            if (first->next == NULL) {
                printf("No one row was created!");
            }
            else {
                print();
            }
            break;
        }
        else if (!strcmp(str, "yes") || !strcmp(str, "y")) {
            printf("\n");
            new_student();
            printf("\n");
            continue;
        }
        else {
            printf("Error in the input, try again\n");
            continue;
        }
    }

    printf("\n");
    cleanup(first);
    printf("\n");

    return 0;
}