Many local clarifications.

Explain about the C library and why system calls are little different
from other library functions.
Add advice to use the debugger and not get delayed by "short cuts".
Why nested function definitions are important.
Typeface for comment text in examples.

c.texi

@@ -93,7 +93,7 @@ If you understand basic concepts of programming but know nothing about
 C, you can read this manual sequentially from the beginning to learn
 the C language.
 
-If you are a beginner to programming, we recommend you first learn a
+If you are a beginner in programming, we recommend you first learn a
 language with automatic garbage collection and no explicit pointers,
 rather than starting with C@.  Good choices include Lisp, Scheme,
 Python and Java.  C's explicit pointers mean that programmers must be
@@ -137,13 +137,23 @@ code will run on.  Where this is the case, we say so.
 
 The C language provides no built-in facilities for performing such
 common operations as input/output, memory management, string
-manipulation, and the like.  Instead, these facilities are defined in
-a standard library, which is automatically available in every C
-program.  @xref{Top, The GNU C Library, , libc, The GNU C Library
-Reference Manual}.
+manipulation, and the like.  Instead, these facilities are provided by
+functions defined in the standard library, which is automatically
+available in every C program.  @xref{Top, The GNU C Library, , libc,
+The GNU C Library Reference Manual}.
+
+GNU/Linux systems use the GNU C Library to do this job.  It is itself
+a C program, so once you know C you can read its source code and see
+how its library functions do their jobs.  Some fraction of the
+functions are implemented as @dfn{system calls}, which means they
+contain a special instruction that asks the system kernel (Linux) to
+do a specific task.  To understand how those are implemented, you'd
+need to read Linux source code instead.  Whether a library function is
+a system call is an internal implementation detail that makes no
+difference for how to call the function.
 
 This manual incorporates the former GNU C Preprocessor Manual, which
-was among the earliest GNU Manuals.  It also uses some text from the
+was among the earliest GNU manuals.  It also uses some text from the
 earlier GNU C Manual that was written by Trevis Rothwell and James
 Youngman.
 
@@ -490,6 +500,10 @@ uses it to explain a few features of the language.  If you already
 know the basic points of C presented in this chapter, you can skim it
 or skip it.
 
+We present examples of C source code (other than comments) using a
+fixed-width typeface, since that's the way they look when you edit
+them in an editor such as GNU Emacs.
+
 @menu
 * Recursive Fibonacci:: Writing a simple function recursively.
 * Stack::               Each function call uses space in the stack.
@@ -556,6 +570,12 @@ comments in the code is tremendously important---they provide
 background information so others can understand the code more quickly.
 @xref{Comments}.
 
+In this manual, we present comment text in the variable-width typeface
+used for the text of the chapters, not in the fixed-width typeface
+used for the rest of the code.  That is to make comments easier to
+read.  This distinction of typeface does not exist in a real file of C
+source code.
+
 @item
 Two kinds of statements, the @code{return} statement and the
 @code{if}@dots{}@code{else} statement.  @xref{Statements}.
@@ -565,8 +585,8 @@ Recursion.  The function @code{fib} calls itself; that is called a
 @dfn{recursive call}.  These are valid in C, and quite common.
 
 The @code{fib} function would not be useful if it didn't return.
-Thus, recursive definitions, to be of any use, must avoid infinite
-recursion.
+Thus, recursive definitions, to be of any use, must avoid
+@dfn{infinite recursion}.
 
 This function definition prevents infinite recursion by specially
 handling the case where @code{n} is two or less.  Thus the maximum
@@ -716,8 +736,8 @@ in the space for the value.  @xref{Integer Overflow}.
 @cindex recursion, drawbacks of
 
 @cindex stack frame
-Recursion has a drawback: there are limits to how many nested function
-calls a program can make.  In C, each function call allocates a block
+Recursion has a drawback: there are limits to how many nested levels of
+function calls a program can make.  In C, each function call allocates a block
 of memory which it uses until the call returns.  C allocates these
 blocks consecutively within a large area of memory known as the
 @dfn{stack}, so we refer to the blocks as @dfn{stack frames}.
@@ -1028,7 +1048,10 @@ certain numeric @dfn{failure codes}.  @xref{Values from main}.
 
 @cindex @code{printf}
 The simplest way to print text in C is by calling the @code{printf}
-function, so here we explain what that does.
+function, so here we explain very briefly what that function does.
+For a full explanation of @code{printf} and the other standard I/O
+functions, see @ref{I/O on Streams, The GNU C Library, , libc, The GNU
+C Library Reference Manual}.
 
 @cindex standard output
 The first argument to @code{printf} is a @dfn{string constant}
@@ -1066,10 +1089,6 @@ The first argument of @code{printf} does not have to be a string
 constant; it can be any string (@pxref{Strings}).  However, using a
 constant is the most common case.
 
-To learn more about @code{printf} and other facilities of the C
-library, see @ref{Top, The GNU C Library, , libc, The GNU C Library
-Reference Manual}.
-
 @node Complete Line-by-Line
 @section Complete Program, Line by Line
 
@@ -1146,6 +1165,13 @@ which starts the GDB debugger (@pxref{Sample Session, Sample Session,
 A Sample GDB Session, gdb, Debugging with GDB}) so you can run and
 debug the executable program @code{fib1}.
 
+Richard Stallman's advice, from personal experience, is to turn to the
+debugger as soon as you can reproduce the problem.  Don't try to avoid
+it by using other methods instead---occasionally they are shortcuts,
+but usually they waste an unbounded amount of time.  With the
+debugger, you will surely find the bug in a reasonable time; overall,
+you will get your work done faster.  The sooner you get serious and
+start the debugger, the sooner you are likely to find the bug.
 
 @xref{Compilation}, for an introduction to compiling more complex
 programs which consist of more than one source file.
@@ -8016,6 +8042,7 @@ the expressions between them may be missing.  A missing expression
 means this loop doesn't use that particular feature of the @code{for}
 statement.
 
+@c ??? You can't do this if START is a declaration.
 Instead of using @var{start}, you can do the loop preparation
 before the @code{for} statement: the effect is the same.  So we
 could have written the beginning of the previous example this way:
@@ -8643,8 +8670,8 @@ This could also be written using a statement expression
 
 Ordinary labels are visible throughout the function where they are
 defined, and only in that function.  However, explicitly declared
-local labels of a block are visible in nested functions declared
-within that block.  @xref{Nested Functions}, for details.
+local labels of a block are visible in nested function definitions
+inside that block.  @xref{Nested Functions}, for details.
 
 @xref{goto Statement}.
 
@@ -11094,9 +11121,10 @@ another.
 @cindex thunks
 
 A @dfn{nested function} is a function defined inside another function.
-The nested function's name is local to the block where it is defined.
-For example, here we define a nested function named @code{square}, and
-call it twice:
+(The ability to do this indispensable for automatic translation of
+certain programming languages into C.)  The nested function's name is
+local to the block where it is defined.  For example, here we define a
+nested function named @code{square}, then call it twice:
 
 @example
 @group
@@ -11109,7 +11137,7 @@ foo (double a, double b)
 @end group
 @end example
 
-The nested function can access all the variables of the containing
+The nested function definition can access all the variables of the containing
 function that are visible at the point of its definition.  This is
 called @dfn{lexical scoping}.  For example, here we show a nested
 function that uses an inherited variable named @code{offset}:
@@ -12958,7 +12986,7 @@ attribute.  @xref{Inline Function Definitions}.
 
 @item gnu_inline
 The @code{gnu_inline} attribute, in a function's declaration or
-definition, specifies to handle the @code{inline} keywprd the way GNU
+definition, specifies to handle the @code{inline} keyword the way GNU
 C originally implemented it, many years before ISO C said anything
 about inlining.  @xref{Inline Function Definitions}.
 @end table