Language: C++

#include <iostream>
#include <vector>
#include <math.h>

class UFO
{
  private:
	double	dist; 	/* ??????????????????????????§????????¢ */
	int		speed;	/* ??\????????? */
	double	rad; 	/* ?????\?§???? */
	int		r;		/* UFO????????? */
	bool	alive;
  public:
	UFO(int x, int y, int r,int v);
	bool	IsAlive();
	double	EchoDist();
	double	EchoRad();
	int		EchoSize();
	void	PastTime();
	void	Hit();
};
int UFOShootingDownOperation();

int main()
{
	while (0 == UFOShootingDownOperation());
	return 0;
}

UFO::UFO(int x, int y, int r,int v) : r(r), speed(v), alive(true)
{
	dist = sqrt(pow(x,2) + pow(y,2));
	rad = acos(x / dist) * 180.0 / M_PI;
	if (y < 0) {
		rad = 360 - rad;
	}
}

bool UFO::IsAlive()
{
	return alive;
}

double	UFO::EchoDist()
{
	return dist;
}

double	UFO::EchoRad()
{
	return rad;
}

int	UFO::EchoSize()
{
	return r;
}

void UFO::PastTime()
{
	if (dist - speed >= 0) {
		dist -= speed;
	}
	else {
		dist = 0;
	}
}

void UFO::Hit()
{
	alive = false;
}

int UFOShootingDownOperation()
{
	using namespace std;
	int		R;				/*??¬?????¶???????¨??????????????????????*/
	int		N;				/*UFO?????°*/
	int 	x0;				/* UFO?????????????????????????????? */
	int		y0;				/* UFO?????????????????????????????? */
	int		r;				/* UFO???????????????????????? */
	int		v;				/* UFO???????????????????????? */
	bool	existsTarget; 	/* ?????????UFO????????£????????????????????? */
	int		aliveUFO;		/* ???????????£???UFO??????????????? */
	double	difRad;			/* UFO?????????????§???¨??¬?????¶?????¨????§?????????????????´?(<=180) */
	vector<UFO>	aliens; 	/* UFO????????± */
	vector<UFO>::iterator itr;
	vector<UFO>::iterator target;
	
	cin >> R >> N;
	
	if (0 == R && 0 == N) {/* ???????????? */
		return -1;
	}
	
	/* ??\??? */
	for (int i = 0; N > i; ++i) {
		cin >> x0 >> y0 >> r >> v;
		aliens.push_back(UFO(x0, y0, r, v));
	}
	/* ????????????1????????????????????? */
	for (itr = aliens.begin(); aliens.end() != itr; ++itr) {
		itr->PastTime();
	}
	/* ???????????????????±?????????¬?????¶??????????°??????????????????? */
	existsTarget = true;
	while (1a) {
		existsTarget = false;
		target = aliens.end();
		for (itr = aliens.begin(); aliens.end() != itr; ++itr) {
			if (false == itr->IsAlive()) {/* ??¬?????¶??????????????????UFO??????????????? */
				continue;
			}
			
			if (itr->EchoDist() > R) {
				if (aliens.end() == target) {
					target = itr;
				}
				else if (target->EchoDist() > itr->EchoDist()){
					target = itr;
				}
				existsTarget = true;
			}
		}
		if (existsTarget) {
			break;
		}
		/* ???????????? */
		for (itr = aliens.begin(); aliens.end() != itr; ++itr) {
			if (false == itr->IsAlive()) {/* ??¬?????¶??????????????????UFO??????????????? */
				continue;
			}
			
			difRad = fabs(target->EchoRad() - itr->EchoRad());
			if (difRad >180) {
				difRad = 360 - difRad;
			}
			if (difRad < 90) {
				if (itr->EchoDist() * sin(difRad * M_PI / 180.0) <= itr->EchoSize()) {
					if (itr->EchoDist() > R) {
						itr->Hit();
					}
				}
			}
			else {
				if (itr->EchoDist() <= itr->EchoSize()) {
					if (itr->EchoDist() > R) {
						itr->Hit();
					}
				}
			}
			
			/*???????????????*/
			itr->PastTime();
		}
	}
	
	aliveUFO = 0;
	for (itr = aliens.begin(); aliens.end() != itr; ++itr) {
		if (true == itr->IsAlive()) {
			++aliveUFO;
		}
	}
	cout << aliveUFO << endl;
	return 0;
}

Compiler output:
a.cc: In function 'int UFOShootingDownOperation()':
a.cc:107:16: error: unable to find numeric literal operator 'operator""a'
  107 |         while (1a) {
      |                ^~