malloc(…) is a function that allocates space ("allocation block") on the heap.
- malloc(…) takes one parameter:  the number of bytes to allocate.
- malloc(…) returns the address of the first byte in the new allocation block.
- malloc(…) returns type void* ("address of anything").
 
sizeof(…) is an operator that gives you the number of bytes needed to store an object.
- sizeof(«VARIABLE») gives you the number of bytes needed to store an object of the
  same type as «VARIABLE».
  - int n = 5;
    sizeof(n) gives you 4 on our platform because n is of type int, and an int occupies
    4 bytes on our platform.
  - Always use sizeof(«VARIABLE»)  (or sizeof(«EXPRESSION»)).
- sizeof(«TYPE») gives you the number of bytes needed to store an object of type «TYPE».
  - sizeof(int) gives you 4 on our platform.
  - DO NOT USE sizeof(«TYPE»)!!!!!!

free(…) is a function that deallocates (="frees") an allocation block.
- free(…) takes one argument: the address of a block allocate by malloc.
- You must call free(…) exactly once for every time you call malloc(…).

TYPECASTS ARE EVIL
           ______
BAD:  int* a_n = (int*) malloc(sizeof(*int));  // Typecasts are EVIL!!!
           ‾‾‾‾‾‾
GOOD: int* a_n = malloc(sizeof(*int));         // no typecast

Example:

char* s = "ABC";
int* a_n = s;  // ERROR --- int* a_n = (int*) s; would silence the error but cause PAIN.