This is bad

this_is_bad.c

/* THIS IS VERY BAD */

#define CONCAT(a, b) CONCAT_(a, b)
#define CONCAT_(a, b) a##b

#define THIS_IS_BAD(test, first, rest, cond, body...) THIS_IS_BAD_2(__COUNTER__, test, first, rest, cond, ##body)
#define THIS_IS_BAD_2(uniq, test, first, rest, cond, body...) THIS_IS_BAD_3(CONCAT(this_is_bad_, uniq), test, first, rest, cond, ##body)
#define THIS_IS_BAD_3(label, test, first, rest, cond, body...) do { \
	if(test) { \
		first(); \
		goto label; \
	} \
	do { \
		rest(); \
	label: \
		body \
		; /* in case body is empty or doesn't end with a semicolon */ \
	} while(cond); \
} while(0)


#include <stdio.h>

void first_time(void) {
	printf("first_time()\n");
}

void other_times(void) {
	printf("other_times()\n");
}

int main(void) {
	int i = 0;
	
	THIS_IS_BAD((i == 0), first_time, other_times, (i < 4), {
		printf("Body: i = %d\n", i);
		++i;
	});
	
	printf("\nAgain, to show that labels aren't being reused.\n\n");
	
	THIS_IS_BAD((i == 4), first_time, other_times, (i >= 0), {
		printf("Reverse body: i = %d\n", i);
		--i;
	});
	
	return 0;
}

this_is_bad.txt

#~/tmp$ clang -std=gnu99 -o this_is_bad this_is_bad.c
#~/tmp$ ./this_is_bad
first_time()
Body: i = 0
other_times()
Body: i = 1
other_times()
Body: i = 2
other_times()
Body: i = 3

Again, to show that labels aren't being reused.

first_time()
Reverse body: i = 4
other_times()
Reverse body: i = 3
other_times()
Reverse body: i = 2
other_times()
Reverse body: i = 1
other_times()
Reverse body: i = 0