#include <stdio.h>
#include <stdlib.h> // For malloc and free

int main(){
  // What is this?
  int * p = (int*)malloc(sizeof(int));
  p = NULL; 
 
  // malloc twice?
  char *char_array;
  char_array = (char*)malloc(50*sizeof(char));
  char_array = (char*)malloc(25*sizeof(char));

  // free twice?
  int* int_array;
  int_array = (int*) malloc (100 * sizeof(int));
  printf("int_array = %p, int_array[0] = %d\n", int_array, int_array[0]);

  free(int_array);
  //free(int_array); // What happens here? compile time error? runtime?
  printf("int_array = %p, int_array[0] = %d\n", int_array, int_array[0]);

  // What happens here?
  int_array[0] = 5;
  int_array[2] = 4;
  printf("int_array = %p, int_array[0] = %d\n", int_array, int_array[0]);
  printf("int_array[2] = %d\n", int_array[2]);

  // old and new things
  int *old_thing = (int*)malloc(sizeof(int));
  printf("old_thing = %p\n", old_thing);
  free(old_thing);
  printf("old_thing = %p after free\n", old_thing);

  int *new_thing = (int*)malloc(sizeof(int));
  printf("new_thing = %p\n", new_thing);
  printf("old_thing = %p\n", old_thing);

  *new_thing = 19;
  *old_thing = 17; // ??
  printf("*new_thing = %d\n", *new_thing);
  printf("*old_thing = %d\n", *old_thing);

  return 0;
}