// Pantea Aria

// introduction to pointers


#include <stdio.h>

int main() {
    int x = 90;
    // what is the address (or reference) of x
    printf ("the address of x in memory is %p\n", &x);
    printf ("the value of x is %d\n", x);
    
    // I can store the address of x in another variable
    // that variable is called a pointer 
    int *ptr;
    // & is called reference/address operator 
    ptr = &x;
    printf("the value of ptr is %p\n", ptr);

    // dereference
    // having access to where the pointer is pointing to
     int y = *ptr;  //same as int y = x;
     printf ("y is the value of where ptr is pointing to %d\n", y);
        
    // change the value of x indirectly
    // directly means e.g x = 100;
    *ptr = 100;   // same as x = 100; not as y = 100;
    printf("the new value of x is %d\n", x);
    printf ("y is %d\n", y);
    y = *ptr;   // y will be 100
    
    
    

    return 0;
}    




















// When we declare a variable in C, where does it live?
// (This leads to the idea of memory locations.)

// What do you think this operator & does in C?
// int x = 10;

// printf("%p\n", &x); // What does this print?  shows some hex value 

// Can a variable store another variable’s memory address?

// What is the value of this variable, and what is its address?
// int a = 5;   value is 5, some hex value &a with %p

// How can we print the address of a? printf ("%p", &a);
// value: printf ("%d", a);

// Can we store this address in another variable? yes, I must declare a pointer

// If we store the address of a in a variable, how can we use it to get the value back?

// int a = 10;
// int *p = &a;
// *p = 20;
// printf("%d\n", a); // What will this print?

// Predict the output and explain:
// int x = 3;
// int y = 4;
// int *p = &x;    //declare a pointer to x, p has the address of x, referencing
// *p = y;   //deferencing
// printf("%d\n", x);
// What’s the difference between p = &x; and *p = x;?

// What is happening here?
// int a = 100;
// int *ptr1 = &a;
// int *ptr2 = ptr1;
// printf("%d\n", *ptr2);