C interview questions

Questions that used to come up in IT interviews, pointers, linked lists, and a few small programs. Each one has a short, clean answer that compiles on GCC.

• const char *p vs char * const p vs const char * const p

  const char *p, char * const p, const char * const p, what each one actually means.

• What does *p++ do?

  Does *p++ move the pointer, or change the value it points at?

• Is *(*(p+i)+j) the same as p[i][j]?

  Why *(*(p+i)+j) == p[i][j], and the num[i] == i[num] trick.

• What operations are valid on pointers?

  The arithmetic and comparisons that are actually legal on pointers.

• Array of pointers vs pointer to an array

  Two things that look alike and behave very differently.

• Delete a node given only a pointer to it

  Deleting a node when all you have is a pointer to it.

• Turn an ordered binary tree into a circular doubly linked list

  Flattening an ordered binary tree into a circular doubly linked list.

• Check for a power of two in one line

  The classic one-line power-of-two check.