Unix and C - Lesson 1

For the first lesson I will talk a bit about Makefiles as well as some introduction to the basics of C.

Makefiles
Often C projects comprise of numerous files that all need to be compiled together to create the final output. Memorizing all the necessary commands to do this can be undesirable, so many people instead use GNU Make and corresponding Makefiles.
The official GNU Make homepage and documentation can be found here:
GNU Make - Free Software Foundation

In a nutshell, the syntax for a Makefile is:

VARIABLE=value
CC=gcc
CFLAGS=-Wall

target: dependency1 dependency2
	command1
	command2

example: example.c example.h
	$(CC) $(CFLAGS) -o example example.c

dependency1:
	echo "hello there"

dependency2:
	echo "how are you?"

/*
   this is a comment.  The compiler will ignore it, but humans can take note of
   it.  The comment ends right here: */
/*
   This is another comment.
   /* nesting (such as this) has no effect.  This comment ends here: */

   We are no longer inside a comment, this will produce an error */

// this is a '//' comment.  It ends at the end of this line.
int x;	// you can start a comment on the same line as code
int y;	/* such as this. */

/* '//' comments within '/* */' comments are ignored.
    // this comment continues after this line
    and ends here: */

// include the system header 'stdio.h':
#include <stdio.h>
// include the system header 'sys/types.h':
#include <sys/types.h>
// include the local header (in the same directory as the .c file) 'hello.h'
#include "hello.h"

// constant MAX
#define MAX	100

// macro to call 'func' on an argument
#define FUNC(n)		func(n)
// another macro, this one using multiple lines (continued lines use the '\' character)
#define MACRO(x, y, z)		for (x = y; x < z; x++) \
					printf("\n");
int main() {
	// use the MAX define:
	int i;
	for (i = 0; i < MAX; i++)
		printf("\n");
	
	// use the MACRO macro
	MACRO(i, 0, 10);
	// the above macro will expand to:
	// for (i = 0; i < 10; i++)
	// 	printf("\n");
}

#define LEN 100
#if (LEN > 99)
#error Recompile with LEN <= 99.
#endif

#if defined(C99)
printf("This code was compiled with a C99 compliant compiler\n");
#endif

#ifdef _WIN32
printf("This code was compiled on Windows\n");
#elif defined(HPUX)
printf("This code was compiled on HP UX\n");
#else
printf("This code was not compiled on Windows or HP UX\n");
#endif

// here's an example where #if is used in the middle of an expression.
// on Windows, LEN must be < 100, on all other platforms, LEN must be > 100.
if (LEN
#ifndef _WIN32
	>
#else
	<
#endif
	100)
	printf("LEN is out of range\n");

// this is often done in header files to prevent multiple inclusion:
#ifndef _SOMEFILE_H_
#define _SOMEFILE_H_
// header contents here
#endif

// hello.c example program

#include <stdio.h>

int main(int argc, char **argv)
{
	printf("Hello, world!\n");
	return 0;
}

// command-line example

#include <stdio.h>

int main(int argc, char **argv)
{
	int i;
	for (i = 0; i < argv; i++)
		printf("argv[%d]=%s\n", i, argv[i]);
	return 0;
}