#include <deque>
#include <stdio.h>
using namespace std;
struct process;
struct simple_int_channel;
struct count_to_three;
struct printer;
struct count_to_n;
typedef int (*process_func)(process *p);
struct process
{
	process_func f;
	int pc;
};
struct simple_int_channel
{
	int value;
	process *waiting;
};
struct count_to_three
{
	process p;
	simple_int_channel *out;
};
struct printer
{
	process p;
	simple_int_channel *in;
};
struct count_to_n
{
	process p;
	simple_int_channel *out;
	int n;
	int c;
};
inline void start(process *p);
inline int resume(process *p);
int count_to_three_f(process *p);
int printer_f(process *p);
int count_to_n_f(process *p);
void run(void);
void step(void);
int main(void);
deque<process *> q;
inline void start(process *p)
{
	q.push_back(p);
}
inline int resume(process *p)
{
	int rv = (*p->f)(p);
	if(rv)
	{
		p->pc = rv;
	}
	return rv;
}
int count_to_three_f(process *p)
{
	count_to_three *d = (count_to_three *)p;
	switch(p->pc)
	{
	case 0:	if(!d->out->waiting)
		{
			p->pc = 1;
			d->out->waiting = p;
			return 0;
		}
	case 1:	d->out->value = 1;
		start(d->out->waiting);
		d->out->waiting = NULL;
		if(!d->out->waiting)
		{
			p->pc = 2;
			d->out->waiting = p;
			return 0;
		}
	case 2:	d->out->value = 2;
		start(d->out->waiting);
		d->out->waiting = NULL;
		if(!d->out->waiting)
		{
			p->pc = 3;
			d->out->waiting = p;
			return 0;
		}
	case 3:	d->out->value = 3;
		start(d->out->waiting);
		d->out->waiting = NULL;
	}
	return 0;
}
int printer_f(process *p)
{
	printer *d = (printer *)p;
	switch(p->pc)
	{
	case 0:	while(1)
		{
			if(d->in->waiting)
			{
				start(d->in->waiting);
			}
			p->pc = 1;
			d->in->waiting = p;
			return 0;
	case 1:		printf("%d\n", d->in->value);
		}
	}
	return 0;
}
int count_to_n_f(process *p)
{
	count_to_n *d = (count_to_n *)p;
	switch(p->pc)
	{
	case 0:	d->c = 1;
		while(d->c <= d->n)
		{
			if(!d->out->waiting)
			{
				p->pc = 1;
				d->out->waiting = p;
				return 0;
			}
	case 1:		d->out->value = d->c;
			start(d->out->waiting);
			d->out->waiting = NULL;
			++ (d->c);
		}
	}
	return 0;
}
void run(void)
{
	while(!q.empty())
	{
		step();
	}
}
void step(void)
{
	process *p = q.front();
	q.pop_front();
	if(resume(p))
	{
		q.push_back(p);
	}
}
int main(void)
{
	simple_int_channel ch ; ch.waiting = NULL;
	count_to_three c3 = { { count_to_three_f, 0 }, &ch };
	printer pr = { { printer_f, 0 }, &ch };
	start(&c3.p);
	start(&pr.p);
	run();
	count_to_n cn = { { count_to_n_f, 0 }, &ch, 10 };
	start(&cn.p);
	run();
	return 0;
}