Jim Stackhouse
                          Graduate Student
                        Computing Sciences
                               Summer 1996

The C Programming Language

The History of C

Insight

Language Structure and Semantics

• Preprocessor Directives
• Data
• Code

Data in C, consists fundamentally of bytes stored in memory, which are not instructions for the cpu, but have some informational content for the program or programmer. These bytes can have more than one interpretation by the code referencing it depending on the context of the reference. The visibility or scope of a particular data(variable) item, to all of the code in a users program, can vary depending on it's physical placement in the program source code file, and by it's definition. Data also has a lifetime characteristic. Some variables are always in existance and others are created and destroyed dynamically as the program/programmer needs them.

Code in C, represents the actual high-level instructions that you want the processor to execute. You can have it interact with the user through devices like the keyboard, screen or printer. The code can and will also interact with different forms of storage, such as ram, rom and external disk, tape or optical media. C is a block structured language, based on the use of code functions. A function is a grouping of processor instructions, following defined rules as defined by C. Functions are called, when their name appears in a C line of code. They may have data passed to them in a pre-defined format, and can return a result of a pre-defined type. Furthermore, several functions relating to a common task, may be grouped together in a separate file for project organization purposes, or for inclusion in some future project. There is one special purpose function that all programs must have. It is the 'main()' function. This is the starting point for the computer when it begins executing your programs code. You may put whatever code or function calls you wish in 'main()'.
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Preprocessor Directives

	#define name string	:performs macros substitutions
		#define	TRUE	1
		#define	FALSE	0

	#error message		:compiler stops and displays line number and message

	#include filename	:compiler will also compile filename at this point
		#include <stdio.h>	searches standard include directory for stdio.h
		#include "stdio.h"	searches working directory for stdio.h

	#if,#ifdef,#ifndef,#else,#elif,#endif
				:selectively compiles enclosed code sections 
				 based on specified condition
		#if constant expression
		  C code...
		#elif 		NOTE: #elif can only be used with #if blocks
		  C code...
		#else
		  C code...
		#endif

	The following can also be used to start an #ifxxx block:
		#ifdef name	:if name is defined by previous #define
		#ifndef name	:if name is not defined by previous #define 

Data Types and Variables

	TYPE			C KEYWORD
	character		char
	integer			int
	floating point		float
	double floating point	double
	valueless		void

	TYPE MODIFIERS(prefixes)
	signed
	unsigned
	short
	long

	[modifier]	type	variable_name;
eg.	unsigned	int	myinteger;
	long		int	mylongint;
			char	mychar;
			float	myfloat;

	struct	AddressRec {
		char	first[15];
		char	last[20];
		int	housenum;
		char	street[20];
	} myaddr, *youraddr;

then...
	myaddr.housenum		:would be the house number.

	youraddr = &myaddr;	(assign pointer to existing myaddr struct)
	youraddr->housenum	:would also be the house number.

	union multi {
		char	c;
		int	i;
		float	f;
	} myunion;

then...
	myunion.c		:is the character representation 
				using the first byte
	myunion.i		:is the integer representation
				using the first 2/4 bytes depends on system
	myunion.f		:is the floating point representation
				using the first 4 bytes

	enum fruit {Apples, Oranges, Peaches};	:Apples=0, Oranges=1, Peaches=2
	enum fruit myfavfruit;
then...
	myfavfruit = Apples

	int x[10];		:creates an array 0 to 9, of ints.
then...
	x[3]			:references the 4th integer in the array.
	x[0]			:references the 1st integer in the array.

	char mystring[] = "This is my string.";

	extern		:used to indicate a variable is
			declared in another file
	auto		:variables declared inside
			of functions get this by default
	register	:requests placement in a cpu register
			for speed
	const		:variable may not be changed by
			the program during execution
	volatile	:the variable may be affected/changed
			by outside influences(clock, etc.)
	static		:keeps local variables in existance
			for duration of program and maintains
			its value, but restricts visibility
			to block where it was defined.

Functions

	int main(int argc, char *argv[]) {
		...your code here...
	}

then...
	argc		:number of arguments
	*argv[1]	:first character of first cmdline argument,
			null terminated
	*argv[0]	:is always the name of the program invoked,
			null terminated

	int	myadd(int a, int b) {
	  int tmp;
	  tmp = a + b;
	  return(tmp);
	}

Operators

Keywords

   auto		break		case		char
   const	continue	default		do
   double	else		enum		extern
   float	for		goto		if
   int		long		register	return
   short	signed		sizeof		static
   struct	switch		typedef		union
   unsigned	void		volatile	while

	auto int j;

	while (j>0) {
	  i++;
	  if (i==10) break;
	}

	switch (i) {
	  case 1:	i++;
	    break;
	  case 2:	i--;
	    break;
	  default:	i=0;
	}

	char ch;

	const char ch;

	while (j>0) {
	  if (j==7) continue;
	  j--;
	}

	switch (i) {
	  case 1:	i++;
	    break;
	  case 2:	i--;
	    break;
	  default:	i=0;
	}

	do {
	  i++;
	} while (i<10);

	double mypaycheck;

	if (i>=0) {
	  i--;
	}
	else {
	  i++;
	}

	enum fruit {apples,peaches,oranges};
	enum fruit myfruit;
	...
	myfruit=peaches;

	extern int varfromotherfile;

	float icecreamcost;

	for (j=1; j<=10; j++) {
	  sum += j;
	}

	goto mylabel;
	...
	label:

	if (k==0) {
	  k=4;
	}
	else {
	  k--;
	}

	int j;

	long int k;

	register int loopcntr;

	int add(int a, int b) {
	  return(a+b);
	}

	int intsize;
	intsize=sizeof(int);

	signed int sint;

	short int shint;

	static int j;

	struct demostruct {
	  int j;
	  char ch;
	} mystruct;

	switch (i) {
	  case 1:	i++;
	    break;
	  case 2:	i--;
	    break;
	  default:	i=0;
	}

	typedef float price;
	price coat;

	union numunion {
	  short int si;
	  long int li;
	  float f;
	} myunion;

	unsigned int uint;

	void *vptr;

	volatile int clocktick;

	while (i>0) {
	  sum+=i;
	}

The ANSI C Header Files

	assert.h	Diagnostics
	ctype.h		Character Handling and Conversion
	float.h		Floating Point Support
	limits.h	Maximum and Minimum Limits
	locale.h	International Support
	math.h		Mathematics
	setjmp.h	Jumps
	signal.h	Signal Handling
	stdarg.h	Variable Number of Arguments
	stddef.h	Standard Definitions
	stdio.h		Input and Output Support
	stdlib.h	General Definitions and Utilities
	string.h	String Handling
	time.h		Time and Date Support

Alphabetic Index to ANSI C Functions

Defenbaugh, JR., Smedley, Richard, C Through Design: An Introduction to ANSI C, Franklin, Beedle & Associates, 1988.
Schildt, Herbert, C: The Pocket Reference, Osborne McGraw-Hill, 1988.
Kernhigan, Brian W., Pike, Rob, The UNIX Programming Environment, Prentice Hall Software Series, 1984.
Borland C++ Programmers Guide, Borland International, 1991,92.