Language: C++

#include <bits/stdc++.h>

using namespace std;

#define TemplateVersion "3.4.0"
// Useful Marcos
//====================START=====================
// Compile use C++11 and above
#ifdef LOCAL
#define debug(args...)                           \
    {                                            \
        string _s = #args;                       \
        replace(_s.begin(), _s.end(), ',', ' '); \
        stringstream _ss(_s);                    \
        istream_iterator<string> _it(_ss);       \
        err(_it, args);                          \
    }
void err(istream_iterator<string> it)
{
}
template <typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args)
{
    cerr << *it << " = " << a << endl;
    err(++it, args...);
}
#define MSG cout << "Finished" << endl
#else
#define debug(args...)
#define MSG
#endif
#if __cplusplus >= 201703L
template <typename... Args>
void readln(Args &... args)
{
    ((cin >> args), ...);
}
template <typename... Args>
void writeln(Args... args)
{
    ((cout << args << " "), ...);
    cout << endl;
}
#elif __cplusplus >= 201103L
void readln()
{
}
template <typename T, typename... Args>
void readln(T &a, Args &... args)
{
    cin >> a;
    readln(args...);
}
void writeln()
{
    cout << endl;
}
template <typename T, typename... Args>
void writeln(T a, Args... args)
{
    cout << a << " ";
    writeln(args...);
}
#endif
#if __cplusplus >= 201103L
#define FOR(_i, _begin, _end) for (auto _i = _begin; _i < _end; _i++)
#define FORR(_i, _begin, _end) for (auto _i = _begin; _i > _end; _i--)
#else
#define FOR(_i, _begin, _end) for (int _i = (int)_begin; _i < (int)_end; _i++)
#define FORR(_i, _begin, _end) for (int _i = (int)_begin; _i > (int)_end; _i--)
#define nullptr NULL
#endif
#if __cplusplus >= 201103L
#define VIS(_kind, _name, _size) \
    vector<_kind> _name(_size);  \
    for (auto &i : _name)        \
        cin >> i;
#else
#define VIS(_kind, _name, _size)    \
    vector<_kind> _name;            \
    _name.resize(_size);            \
    for (int i = 0; i < _size; i++) \
        cin >> _name[i];
#endif
// alias
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define tcase() \
    int T;      \
    cin >> T;   \
    FOR(kase, 1, T + 1)
// Swap max/min
template <typename T>
bool smax(T &a, const T &b)
{
    if (a > b)
        return false;
    a = b;
    return true;
}
template <typename T>
bool smin(T &a, const T &b)
{
    if (a < b)
        return false;
    a = b;
    return true;
}
// ceil divide
template <typename T>
T cd(T a, T b)
{
    return (a + b - 1) / b;
}
// min exchange
template <typename T>
bool se(T &a, T &b)
{
    if (a < b)
        return false;
    swap(a, b);
    return true;
}
// A better MAX choice
const int INF = 0x3f3f3f3f;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef set<int> si;
typedef vector<string> cb;
//====================END=====================

// Constants here
const double EPS = 1e-8;
const double PI = acos(-1);

typedef double db;

int sgn(db x)
{
    if (abs(x) < EPS)
        return 0;
    if (x < 0)
        return -1;
    return 1;
}

inline db sqr(db x) { return x * x; }

// Point/Vector
struct Point
{
    db x, y;

    Point() : x(1e-18), y(1e-18) {}

    Point(db _x, db _y) : x(_x + 1e-18), y(_y + 1e-18) {}

    bool operator==(const Point &p)
    {
        return sgn(x - p.x) == 0 && sgn(y - p.y) == 0;
    }

    bool operator<(const Point &p)
    {
        int c = sgn(x - p.x);
        if (c)
            return c == -1;
        return sgn(y - p.y) == -1;
    }

    Point operator+(const Point &p) { return Point(x + p.x, y + p.y); }
    Point operator-(const Point &p) { return Point(x - p.x, y - p.y); }
    Point operator*(db d) { return Point(x * d, y * d); }
    Point operator/(db d) { return Point(x / d, y / d); }

    db operator^(const Point &p) { return x * p.y - y * p.x; }
    db operator*(const Point &p) { return x * p.x + y * p.y; }

    db dis(const Point &p) { return (*this - p).len(); }
    db alpha() { return atan2(y, x); }

    Point unit() { return *this / len(); }

    Point rotac() { return Point(-y, x); }
    Point rotcl() { return Point(y, -x); }

    Point rot(Point p, db angle)
    {
        Point v = *this - p;
        db c = cos(angle), s = sin(angle);
        return Point(p.x + v.x * c - v.y * s, p.y + v.x * s + v.y * c);
    }

    db len() { return hypot(x, y); }
    db len2() { return x * x + y * y; }

    db rad(Point a, Point b)
    {
        Point ap = a - *this, bp = b - *this;
        return abs(atan2(abs(ap ^ bp), ap * bp));
    }

    void read() { cin >> x >> y; }
    void write() { cout << '(' << x << ", " << y << ")\n"; }
};

// Line
struct Line
{
    Point s, e;

    Line(){};

    Line(Point _s, Point _e) : s(_s), e(_e) {}

    Line(Point p, db angle)
    {
        s = p;
        if (sgn(angle - PI / 2))
            e = (s + Point(1, tan(angle)));
        else
            e = (s + Point(0, 1));
    }

    //ax+by+c=0
    Line(db a, db b, db c)
    {
        if (sgn(a) == 0)
        {
            s = Point(0, -c / b);
            e = Point(1, -c / b);
        }
        else if (sgn(b) == 0)
        {
            s = Point(-c / a, 0);
            e = Point(-c / a, 1);
        }
        else
        {
            s = Point(0, -c / b);
            e = Point(1, -(c + a) / b);
        }
    }

    db len() { return s.dis(e); }
    db angle()
    {
        db ans = atan2(e.y - s.y, e.x - s.x);
        if (sgn(ans) == -1)
            ans += PI;
        if (sgn(ans - PI) == 0)
            ans -= PI;
        return ans;
    }

    // 1 -> On Counter-clockwise
    // 2 -> On Clockwise
    // 3 -> On Line Back
    // 4 -> On Line Front
    // 5 -> On Segment
    int relation(Point p)
    {
        Point x = p - s, y = e - s;
        int c = sgn(x ^ y);
        if (c < 0)
            return 1;
        if (c > 0)
            return 2;
        if (sgn(x * y) < 0)
            return 3;
        if (sgn((s - p) * (b - p)) > 0)
            return 4;
        return 5;
    }

    bool parallel(Line l) { return sgn((e - s) ^ (l.e - l.s)) == 0; }

    // 0 -> Formal Intersection
    // 1 -> Informal
    // 2 -> Not Intersect
    int crossSS(Line l)
    {
        int d1 = sgn((e - s) ^ (l.s - s));
        int d2 = sgn((e - s) ^ (l.e - s));
        int d3 = sgn((l.e - l.s) ^ (s - l.s));
        int d4 = sgn((l.e - l.s) ^ (e - l.s));
        if ((d1 ^ d2) == -2 && (d3 ^ d4) == -2)
            return 2;
        return (d1 == 0 && sgn((l.s - s) * (l.s - e)) <= 0) ||
               (d2 == 0 && sgn((l.e - s) * (l.e - e)) <= 0) ||
               (d3 == 0 && sgn((s - l.s) * (s - l.e)) <= 0) ||
               (d4 == 0 && sgn((e - l.s) * (e - l.e)) <= 0);
    }

    // 0 -> Formal Intersection
    // 1 -> Informal
    // 2 -> Not Intersect
    int crossLS(Line l)
    {
        int d1 = sgn((e - s) ^ (l.s - s));
        int d2 = sgn((e - s) ^ (l.e - s));
        if ((d1 ^ d2) == -2)
            return 2;
        return (d1 == 0 || d2 == 0);
    }

    // 0 -> Parallel
    // 1 -> Same
    // 2 -> Intersect
    int crossLL(Line l)
    {
        if (this->parallel(l))
            return l.relation(s) == 3;
        return 2;
    }

    Point crossP(Line l)
    {
        db a1 = (l.e - l.s) ^ (s - l.s);
        db a2 = (l.e - l.s) ^ (e - l.s);
        return Point((s.x * a2 - e.x * a1) / (a2 - a1), (s.y * a2 - e.y * a1) / (a2 - a1));
    }

    db disPL(Point p) { return abs((p - s) ^ (e - s)) / len(); }
    db disPS(Point p)
    {
        if (sgn((p - s) * (e - s)) < 0 || sgn((p - e) * (s - e)) < 0)
            return min(p.dis(s), p.dis(e));
        return disPL(p);
    }
    db disSS(Line l) { return min(min(disPS(l.s), disPS(l.e)), min(l.disPS(s), l.disPS(e))); }

    Point proj(Point p) { return s + ((e - s) * ((e - s) * (p - s))) / ((e - s).len2()); }
    Point refl(Point p)
    {
        Point q = proj(p);
        return Point(2 * q.x - p.x, 2 * q.y - p.y);
    }

    bool operator==(Line l) { return s == l.s && e == l.e; }

    void adjust()
    {
        if (e < s)
            swap(s, e);
    }

    void read()
    {
        s.read();
        e.read();
    }

    void write()
    {
        cout << "Line:\n";
        s.write();
        e.write();
    }
};

// Pre-Build Function
inline void build()
{
}

// Actual Solver
inline void solve()
{
    Line l;
    l.read();
    int q;
    cin >> q;
    while (q--)
    {
        Point p;
        p.read();
        int re = l.relation(p);
        if (re == 1)
            cout << "COUNTER_CLOCKWISE\n";
        else if (re == 2)
            cout << "CLOCKWISE\n";
        else if (re == 3)
            cout << "ONLINE_BACK\n";
        else if (re == 4)
            cout << "ONLINE_FRONT\n";
        else
            cout << "ON_SEGMENT\n";
    }
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

#ifdef LOCAL
    clock_t _begin = clock();
#endif

    build();
    solve();

#ifdef LOCAL
    cerr << "Time elapsed: " << (double)(clock() - _begin) * 1000 / CLOCKS_PER_SEC << "ms." << endl;
#endif

    return 0;
}


Compiler output:
a.cc: In member function 'int Line::relation(Point)':
a.cc:277:28: error: 'b' was not declared in this scope; did you mean 'db'?
  277 |         if (sgn((s - p) * (b - p)) > 0)
      |                            ^
      |                            db