C++ Coroutines kinda like Unity but shitier

CppCoroutine.cpp

// c++ Coroutines by tim.tili.sabo@gmail.com
// using modified coroutines.hpp from boost

#include <stdio.h>
#include <string.h>
#include "SDL/SDL.h"
#include "CoroutineTest.h"
#include <boost/foreach.hpp>

namespace { // anonymous namespace

	class TestCoro : coroutine {
		// all state should be put here
		int& a;
	public:
		TestCoro(int& outsideVar) : coroutine(), a(outsideVar) {}
		void operator()() {
			if (is_complete()) {
				return;
			}
			reenter (this) // really want to get rid of this line, its so ugly...
			{
				// normal yield skips until next frame
				a = 0;
				printf("some code before yield  a=%i\n", a);
				yield;
				a += 1;
				printf("some other code after yield  a=%i\n", a);
				yield;

				a += 1;
				printf("wait for time test %i\n", SDL_GetTicks());
				printf("a=%i\n", a);
				WaitForSeconds(2.0f);

				a += 1;
				printf("waited 2 seconds %i\n", SDL_GetTicks());
				printf("a=%i\n", a);
				WaitForSeconds(4.0f);

				a += 1;
				printf("waited 4 seconds %i\n", SDL_GetTicks());
				printf("a=%i\n", a);

				// this yield until someting is done, handy for tweens or ai for example
				while (a < 40) {
					a++;
					printf("a=%i\n", a);
					yield; // normal yield skips until next frame
				}

				printf("coroutine done!\n");
			}
		}
	};
}


void Update() {
}

void Render() {
}


int main(int argc, char *argv[]) {
	int testVar = -1;

	// we want the value testVar to get to 40 using a coroutine
	StartCoroutine(TestCoro(testVar)); // start a new coroutine and stop at the first yield

    // game loop
	while (testVar != 40) {
		Update();
		Render();

		// delete finished coroutines
		coroutine::currentCoroutines.erase(remove_if(coroutine::currentCoroutines.begin(), coroutine::currentCoroutines.end(), DeleteCoroutinePredicate), coroutine::currentCoroutines.end());
		// loop trough all existing coroutines and give them a go.
		BOOST_FOREACH(boost::shared_ptr<coroutine> coro, coroutine::currentCoroutines) {
			(*coro)();
		}
	}

	printf("finished main loop!\n");
	return 0;
}


output:

some code before yield  a=0
some other code after yield  a=1
wait for time test 122
a=2
waited 2 seconds 2131
a=3
waited 4 seconds 6148
a=4
a=5
a=6
a=7
a=8
a=9
a=10
a=11
a=12
a=13
a=14
a=15
a=16
a=17
a=18
a=19
a=20
a=21
a=22
a=23
a=24
a=25
a=26
a=27
a=28
a=29
a=30
a=31
a=32
a=33
a=34
a=35
a=36
a=37
a=38
a=39
a=40
coroutine done!
finished main loop!

Coroutine like Unity using C++ and boost coroutine2:
https://github.com/exawon/CoroBehaviour