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

#include <time.h> //time()


struct Student
{	
	int id;
	float gpa;
	char* name;
};

void print_std (struct Student std){
	printf("Name: %s\n", std.name);
	printf("ID: %d\n", std.id);
	printf("GPA: %f\n", std.gpa);
	return;
}

void sort_first_two (void** arr, int n, int (*cmp) (void* a, void* b)){
	if (cmp(arr[0], arr[1]) == 1){
		//swap the two element
		void* temp = arr[0];
		arr[0] = arr[1];
		arr[1] = temp;
		return;
	}
	return;
}

int compare_int(void* a, void* b){
	int* ai = a, *bi = b;
	if (*ai > *bi) 
		return 1;
	return 0;
}

int compare_std(void* a, void* b){
	struct Student* s1 = a, *s2 = b;
	if (s1->id > s2->id)
		return 1;
	return 0;
}

int main()
{
	srand(time(NULL));

	int size = 10;

	int** arr = malloc(sizeof(int*) * size);

	//populate the array
	for (int i = 0; i < size; ++i)
	{
		arr[i] = malloc(sizeof(int));
		*(arr[i]) = rand() % 51; //0-50
	}

	//print the array
	for (int i = 0; i < size; ++i)
	{
		printf("%d ", *(arr[i]));
	}
	printf("\n");
	
	sort_first_two((void**)arr, size, compare_int);

	//print the array
	for (int i = 0; i < size; ++i)
	{
		printf("%d ", *(arr[i]));
	}
	printf("\n");

	struct Student** std_arr = malloc (sizeof(struct Student*) *2);

	std_arr[0] = malloc (sizeof(struct Student));
	std_arr[0]->id = 5678;
	std_arr[0]->gpa = 3.0;
	std_arr[0]->name = "name1";

	std_arr[1] = malloc (sizeof(struct Student));
	std_arr[1]->id = 1234;
	std_arr[1]->gpa = 4.0;
	std_arr[1]->name = "name2";

	print_std (*(std_arr[0]));
	print_std (*(std_arr[1]));
	printf("\n");

	sort_first_two((void**)std_arr, 2, compare_std);

	print_std (*(std_arr[0]));
	print_std (*(std_arr[1]));
	printf("\n");


	for (int i = 0; i < size; ++i)
	{
		free(arr[i]);
		arr[i] = NULL;
	}
	free(arr);
	arr = NULL;

	free(std_arr[0]);
	free(std_arr[1]);
	free (std_arr);
	std_arr = NULL;

	return 0;
}