Cryptic C code?

[VLD/VMB]

First, the (char) in the while(expression) is NOT converted to an (int)
in case 3; it is tested against zero directly.  In case 2 it is
converted to (int) for the comparison against '\0'.

I think case 2 is certainly more readable, but as the book says, you
need to learn to read things like case 3 since a lot of code is like
that.  More usually one will see something like
	char *s;
	...
	while ( *s++ )
		...
This really is a standard C idiom, although I don't recommend writing
code that way.  I personally prefer to distinguish between Boolean
expressions (such as comparisons) and arithmetic expressions, using
strictly Boolean expressions as conditions.  Thus:
	while ( *s++ != '\0' )
or even
	while ( (int)*s++ != '\0' )
The typecast is perhaps overly fussy; it is not required by the
language rules and may detract from readability.

Tests for NULL pointers and flags often are written
	if ( p )
		...
	if ( flag & BIT )
		...
rather than
	if ( p != NULL )
		...
	if ( (flag & BIT) != 0 )
		...
(I prefer the latter.)  Get used to it..