#define

ConditionalCompilation.c

#define DEBUG_MODE

#ifdef UNICODE
#define TCHAR wchar_t
#else
#define TCHAR char
#endif

#ifdef _DEBUG
	#define LOG(format, val) printf(format, val)
#else
	#define LOG(format, val)
#endif

TCHAR string[10];

void main()
{
	int val = 10;

// in real life, use "_DEBUG" instead of "DEBUG_MODE" (prefdefined in project properties)
#if defined DEBUG_MODE
	printf("val = %d\n", val);
#endif

	val += 20;
	// ...
	--val;
	// ...

#ifdef DEBUG_MODE
	printf("val = %d\n", val);
#endif

	LOG("val = %d\n", val);

#ifndef DEBUG_MODE // #if !defined
	// Release mode code
#endif
}

define.c

#include <string.h>

#define PI 3.14
#define MAX(a, b) a > b ? a : b
#define MAX_FIXED(a, b) (((a) > (b)) ? (a) : (b))

#define MULTI_LINE int variable = 0; \
        variable++; \
		variable += 5;

#define INT_VAR(name) int int_##name;
#define STRUCT(name) typedef struct \
{                                   \
	int name##_id;                  \
	char name##_value[10];			\
} ##name;

int Max(int a, int b)
{
	return a > b ? a : b;
}

int f()
{
	return 10;
}

int g()
{
	static s = 20;

	s -= 7;

	return s;
}

void main()
{
	double radius = 10.0;

	double circumference = 2 * PI * radius;

	double x = 1.1, y = 2.2;

	int maxint = Max(x, y); // converts to int, not good enough

	maxint = MAX(17, -37);
	// replaced with:
	maxint = 17 > -37 ? 17 : 37;

	double maxdouble = MAX(x, y);
	// replaced with:
	maxdouble = x > y ? x : y;

	maxint = MAX(10, 5) + 2; // returns 10 instead of 12!?
	// replaced with:
	maxint = 10 > 5 ? 10 : 5 + 2; // plus is stronger than ternary operator
	maxint = MAX_FIXED(10, 5) + 2; // works fine

	maxint = MAX_FIXED(f(), g()); // max of 10 and 13 is 6 !?

	MULTI_LINE;

	INT_VAR(myVar);
	int_myVar = 10;

	STRUCT(Object);

	Object o;
	o.Object_id = 10;
	strcpy(o.Object_value, "something");
}