C Essentials basics

Essential CBy Nick ParlanteCopyright 1996-2003, Nick Parlante
This Stanford CS Education document tries to summarize all the basic features of the C
language. The coverage is pretty quick, so it is most appropriate as review or for someone
with some programming background in another language. Topics include variables, int
types, floating point types, promotion, truncation, operators, control structures (if, while,
for), functions, value parameters, reference parameters, structs, pointers, arrays, the pre-
processor, and the standard C library functions.
The most recent version is always maintained at its Stanford CS Education Library URL
http://cslibrary.stanford.edu/101/. Please send your comments to
[email protected].
I hope you can share and enjoy this document in the spirit of goodwill in which it is given
away -- Nick Parlante, 4/2003, Stanford California.
Stanford CS Education LibraryThis is document #101, Essential C, in the StanfordCS Education Library. This and other educational materials are available for free athttp://cslibrary.stanford.edu/. This article is free to be used, reproduced, excerpted,retransmitted, or sold so long as this notice is clearly reproduced at its beginning.Table of Contents
Introduction.........................................................................................pg. 2
Where C came from, what is it like, what other resources might you look at.
Section 1Basic Types and Operators..........................................pg. 3
Integer types, floating point types, assignment operator, comparison operators,
arithmetic operators, truncation, promotion.
Section 2Control Structures........................................................pg. 11
If statement, conditional operator, switch, while, for, do-while, break, continue.
Section 3Complex Data Types.....................................................pg. 15
Structs, arrays, pointers, ampersand operator (&), NULL, C strings, typedef.
Section 4Functions........................................................................pg. 24
Functions, void, value and reference parameters, const.
Section 5Odds and Ends..............................................................pg. 29
Main(), the .h/.c file convention, pre-processor, assert.
Section 6Advanced Arrays and Pointers....................................pg. 33
How arrays and pointers interact. The [ ] and + operators with pointers, base
address/offset arithmetic, heap memory management, heap arrays.
Section 7Operators and Standard Library Reference..............pg. 41
A summary reference of the most common operators and library functions.
The C Language
C is a professional programmer's language. It was designed to get in one's way as little as
possible. Kernighan and Ritchie wrote the original language definition in their book, The
C Programming Language (below), as part of their research at AT&T. Unix and C++
emerged from the same labs. For several years I used AT&T as my long distance carrier
in appreciation of all that CS research, but hearing "thank you for using AT&T" for the
millionth time has used up that good will.

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Some languages are forgiving. The programmer needs only a basic sense of how things
work. Errors in the code are flagged by the compile-time or run-time system, and the
programmer can muddle through and eventually fix things up to work correctly. The C
language is not like that.
The C programming model is that the programmer knows exactly what they want to do
and how to use the language constructs to achieve that goal. The language lets the expert
programmer express what they want in the minimum time by staying out of their way.
C is "simple" in that the number of components in the language is small-- If two language
features accomplish more-or-less the same thing, C will include only one. C's syntax is
terse and the language does not restrict what is "allowed" -- the programmer can pretty
much do whatever they want.
C's type system and error checks exist only at compile-time. The compiled code runs in a
stripped down run-time model with no safety checks for bad type casts, bad array indices,
or bad pointers. There is no garbage collector to manage memory. Instead the
programmer mangages heap memory manually. All this makes C fast but fragile.
Analysis -- Where C Fits
Because of the above features, C is hard for beginners. A feature can work fine in one
context, but crash in another. The programmer needs to understand how the features work
and use them correctly. On the other hand, the number of features is pretty small.
Like most programmers, I have had some moments of real loathing for the C language. It
can be irritatingly obedient -- you type something incorrectly, and it has a way of
compiling fine and just doing something you don't expect at run-time. However, as I have
become a more experienced C programmer, I have grown to appreciate C's straight-to-the
point style. I have learned not to fall into its little traps, and I appreciate its simplicity.
Perhaps the best advice is just to be careful. Don't type things in you don't understand.
Debugging takes too much time. Have a mental picture (or a real drawing) of how your C
code is using memory. That's good advice in any language, but in C it's critical.
Perl and Java are more "portable" than C (you can run them on different computers
without a recompile). Java and C++ are more structured than C. Structure is useful for
large projects. C works best for small projects where performance is important and the
progammers have the time and skill to make it work in C. In any case, C is a very popular
and influential language. This is mainly because of C's clean (if minimal) style, it's lack
of annoying or regrettable constructs, and the relative ease of writing a C compiler.
Other Resources
•The C Programming Language, 2nd ed., by Kernighan