increment.c

#include <stdio.h>

#define binary_to_gray_code(binary) ((binary)^(binary)>>1)

int fputb(unsigned int input,unsigned int digit,FILE *output)
{
	if(digit){
		fputb(input>>1,digit-1,output);
		fputc('0'+(input&1),stdout);
	}
	return input;
}

unsigned int true_bit_counter(unsigned int input)
{
	if(!input){
		return 0;
	}
	else{
		return (input&1)+true_bit_counter(input>>1);
	}
}

unsigned int gray_code_increment(unsigned int input)
{
	if(!(true_bit_counter(input)&1)){
		return input^1;
	}
	else{
		return gray_code_increment(input>>1)<<1|(input&1);
	}
}

int main(void)
{
	unsigned int gray_code = binary_to_gray_code(0);
	while(gray_code != binary_to_gray_code(64)){
		fputb(gray_code,6,stdout);
		fputc('\n',stdout);
		gray_code = gray_code_increment(gray_code);
	}
	return 0;
}