#include <stdio.h>
 #include <stdlib.h>
 
 /* A short description of the function, if necessary
  */
 int main (int args, char *argv[]) {

    int *ptr; // here, star means pointer type
    int a = 5;
    
    ptr = &a; // ptr now had the value of the address of a.
    
    // Here, star means follow the pointer and access what is
    // at the end of it.
    printf( "a is %d and ptr points to %d\n", a, *ptr );
    printf( "ptr has the value %p\n", ptr );
    printf( "ptr is at address %p on the stack\n", &ptr );
    
    ptr = malloc( sizeof(int) );
    *ptr = 6;
    printf( "a is %d and ptr points to %d\n", a, *ptr );
    printf( "ptr has the value %p\n", ptr );
    
    // create a memory leak
    ptr = &a;
    
    ptr = malloc( sizeof(int) );
    *ptr = 7;
    printf( "ptr has the value %p\n", ptr );
    free( ptr ); // this time, free the memory first.

    
    // so now, the 7's spot is available for more mallocing but the
    // 6's spot never will be.
    
    // dereferencing a freed pointer is not something we are supposed to do
    // it leads to undefined behavior
    // I wish it caused an error, but it doesn't :(
    // ptr is what we call a "dangling reference"
    printf( "after free, ptr has the value %p\n", ptr );
    printf( "a is %d and ptr points to %d\n", a, *ptr );
    
    // malloc tends to reuse memory spots, so it is likely to return 
    // the address that ptr just freed (no guarantees, though!)
    int *ptr2 = (int *)malloc( sizeof(int) );
    printf( "ptr2 has the value %p\n", ptr2 );
    *ptr2 = 8;
    printf( "ptr points to %d and ptr2 points to %d\n", *ptr, *ptr2 );
    if (ptr == ptr2) {
        printf( "ptr and ptr2 have the same value, so point to the same address\n" );
        printf( "*ptr is %d and *ptr2 is %d\n", *ptr, *ptr2 );
    }
    else {
        printf( "ptr and ptr2 have addresses %ld far apart\n", ptr-ptr2 );
    }
    
//     ptr = malloc( sizeof(int) );
//     *ptr = 8;
//     printf( "a is %d and ptr points to %d\n", a, *ptr );
//     printf( "ptr has the value %p\n", ptr );
}