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


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;
}

int main(int argc, char const *argv[])
{
	//I/O
	int var = 20;
	printf("the value of var is: %d\n", var);

	printf("Enter a new value of var: ");
	scanf("%d", &var); //don't forget the '&'

	printf("now the new value of var is: %d\n", var);

	//structure
	struct Student s;
	s.id = 123456;
	s.gpa = 4.0;
	s.name = "Some Student";

	print_std(s);


	//pointers
	int * p1 = &var;
	int** p2 = &p1;

	//int
	printf("content of var: %d\n", var);
	printf("deference of p1: %d\n", *p1);
	printf("double deference of p2: %d\n", **p2);

	//int*
	printf("addr of var: %p\n", &var);
	printf("content of p1: %p\n", p1);
	printf("deference of p2: %p\n", *p2);

	//int **
	printf("addr of p1: %p\n", &p1);
	printf("content of p2: %p\n", p2);

	//int *** 
	printf("addr of p2: %p\n", &p2);


	//void *
	void* v_ptr = &var;
	//printf("deference v_ptr w/o casting: %d\n", *v_ptr);// error!!
	printf("deference v_ptr w/ casting: %d\n", *((int*)v_ptr));

	v_ptr = &s;
	print_std(*((struct Student*)v_ptr));

	struct Student *s_ptr = v_ptr;
	print_std(*s_ptr);


	int *array = malloc(100 * sizeof(int));

	free(array);
	array = NULL;

	//c-strings
	char* name = "Roger"; //constant c-string

	//name[0] = 'o'; //seg fault

	const char* name2 = "some name";
	//name2[0] = 'j'; //compiling error 


	//char* str = malloc(sizeof(char) * 64);
	char str[64] = "hello";

	// for static array, the &str, &str[0], str --> same addr
	// for dynamic array, the &str[0], str --> same addr, but &str is different
	// cannot get the size of a dynamic array using sizeof()

	//char* str = malloc(sizeof(char) * 64);

	//str = "hello";

	printf("size of str: %d\n", sizeof(str));
	printf("strlen of str: %d\n", strlen(str));

	//str = "hello world";

	//printf("strlen of str: %d\n", strlen(str));








	


	return 0;
}