Лабараторна 11, варіант 6(стеки)

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


struct Group peek();
void push(struct Group value);
void show_item(struct Group item);
void show_items();
void add_item();
void pop();


struct Group
{
float students;
float there;
float missing;
};


struct Stack
{
struct Group data;
struct Stack *next;
} *head;
int stack_size = 10;
int stack_length = 0;



int menu()
{
int answer;
printf("Menu:\n");
printf("1. Push\n");
printf("2. Pop\n");
printf("3. Peek\n");
printf("4. Show items\n");
printf("0. Exit\n");
printf(">\n");
scanf("%d", &answer);
return answer;
}

int main()

{
        int answer = menu();
    while (answer)
{
    switch (answer)
{
  case 1:
{
    add_item();
    printf("Push done!\n");
    break;
}
  case 2:
    pop();
    printf("Pop done!\n");
    break;
  case 3:
    show_item(peek());
    break;
  case 4:
    show_items();
    break;
    default:
    printf("Error number!!!\n");
    break;
}
    answer = menu();
}
    system("pause");
    return 0;
}


void add_item()
{
struct Group new_item;
printf("Enter students, there, missing:\n");
scanf("%f%f%f", &new_item.students, &new_item.there, &new_item.missing);
push(new_item);
}

void show_item(struct Group item)
{
printf("Students: %s\n", item.students);
printf("There: %f\n", item.there);
printf("Missing: %f\n", item.missing);
}

void show_items()
{
        struct Stack *current = head;
        if (current == NULL)
        {
                printf("Stack is empty!\n");
        }
        else
        {
                int counter = 1;
                while (current != NULL)
                {
                        if (current->data.missing > 6)
                        {
                                printf("#%d:\n", counter);
                                show_item(current->data);
                                counter++;
                        }
                        current = current->next;
                }
                if (counter == 1)
                {
                        printf("Not found!\n");
                }
        }
}
void push(struct Group value)
{
  if (stack_length == stack_size)
{
  printf("Error: Stack overflow\n");
   return;
}
  if (head == NULL)
{
  head = malloc(sizeof(struct Stack));
  head->data = value;
  head->next = NULL;
  stack_length = 1;
}
  else
{
struct Stack *new_element = malloc(sizeof(struct Stack));
 new_element->data = value;
 new_element->next = head;
 head = new_element;
 stack_length++;
}
}

void pop()
{
  if (head == NULL)
{
  return;
}

  if (head->next == NULL)
{
 free(head);
 head = NULL;
 stack_length = 0;
}
  else
{
struct Stack *buffer = head;
 head = head->next;
 free(buffer);
 stack_length--;
}
}

struct Group peek()
{
 if (head != NULL)
{
 return head->data;
}


else
{
struct Group empty;
empty.students = 0;
empty.there = 0;
empty.missing = 0;
return empty;
}
}