// 24T3 COMP1511 Week 5 Lecture 2
// Introduction to basic pointer concepts
// Address of operator &
// Declaring and initialised pointer variables
// Dereferencing pointer variables

#include <stdio.h>

int main(void) {

    // Decare and initialise a normal int variable called 'x'
    int x = 2;   

    // Print the address and value of x
    printf("The int that x stores (x): %d\n", x);
    printf("The address of x (&x): %p\n", &x);
    
    // // Declare a pointer variable 'x_ptr' and assign the address of 'x' to it
    int *x_ptr = &x;

    // Print the addresses and value of x_ptr
    printf("The address that x_ptr stores (x_ptr): %p\n", x_ptr);
    printf("The address of x_ptr (&x_ptr): %p\n", &x_ptr);
    
    // Dereference 'x_ptr'
    printf("The int we get when we dereference x_ptr (*x_ptr): %d\n", *x_ptr);
    
    // Modify x indirectly via our pointer
    *x_ptr = 99;
    printf("x:%d   *x_ptr:%d \n", x, *x_ptr);

    // // make num_ptr points to where x_ptr is pointing at
    int *num_ptr = x_ptr; 


    // // // What does num_ptr contain
    printf("num_ptr: %p x_ptr: %p &x: %p\n", num_ptr, x_ptr, &x);

    // Indirectly modify x via num_ptr
    *num_ptr = 10; // x = 10;
    printf("x: %d *x_ptr: %d *num_ptr: %d\n", x, *x_ptr, *num_ptr);

    // num_ptr is pointing somewhere else now
    int y = 4;
    num_ptr = &y;
    printf("*num_ptr %d\n", *num_ptr);
    y = 99;
    printf("*num_ptr %d\n", *num_ptr);


    
    // // INVALID C CODE
    //double d = 1.5;
    //num_ptr = &d;

    num_ptr = NULL;
    printf("%p\n", num_ptr);
    printf("%d\n", *num_ptr);
     
    if (num_ptr != NULL) {
         printf("%p %d\n", num_ptr, *num_ptr);
    }
    return 0;     
}