#define C_MAX_2(a, b)                         (((a) > (b)) ? (a) : (b))
#define C_MAX_3(a, b, c)                      C_MAX_2((C_MAX_2((a),(b))), (c))
#define C_MAX_4(a, b, c, d)                   C_MAX_2((C_MAX_2((a),(b))),
                                                      (C_MAX_2((c),(d))))
#define C_MAX_5(a, b, c, d, e)                C_MAX_2((C_MAX_3((a),(b), (c))),
                                                      (C_MAX_2((d),(e))))

#define MAX_2(n1, n2) (n1 > n2 ? n1 : n2)
#define MAX_3(n1, n2, n3)         MAX_2(n1, MAX_2(n2, n3))
#define MAX_4(n1, n2, n3, n4)     MAX_2(n1, MAX_3(n2, n3, n4))
#define MAX_5(n1, n2, n3, n4, n5) MAX_2(n1, MAX_4(n2, n3, n4, n5))

#define COUNTARGS(...) GET21ST(__VA_ARGS__,COUNTDOWN())
#define COUNTDOWN() 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0
#define GET21ST(a20,a19,a18,a17,a16,a15,a14,a13,a12,a11,a10,a9,a8,a7,a6,a5,a4,a3,a2,a1,a,...) a

#define EVAL(...)  EVAL1(EVAL1(EVAL1(__VA_ARGS__)))
#define EVAL1(...) EVAL2(EVAL2(EVAL2(__VA_ARGS__)))
#define EVAL2(...) EVAL3(EVAL3(EVAL3(__VA_ARGS__)))
#define EVAL3(...) EVAL4(EVAL4(EVAL4(__VA_ARGS__)))
#define EVAL4(...) EVAL5(EVAL5(EVAL5(__VA_ARGS__)))
#define EVAL5(...) __VA_ARGS__

#define VANISH()
#define OBSTRUCT(...) __VA_ARGS__ VANISH()
#define COUNTDOWN() 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0
#define COUNTARGS(...) EVAL(OBSTRUCT(GET21ST)(__VA_ARGS__,COUNTDOWN()))
#define GET21ST(a20,a19,a18,a17,a16,a15,a14,a13,a12,a11,a10,a9,a8,a7,a6,a5,a4,a3,a2,a1,a,...) a

#define MAX_1(n) n
#define MAX_2(a,b) ((a)>(b)?(a):(b))
#define MAX_3(a,...) MAX_2(a,MAX_2(__VA_ARGS__))
#define MAX_4(a,...) MAX_2(a,MAX_3(__VA_ARGS__))
...
#define MAX_20(a,...) MAX_2(a,MAX_19(__VA_ARGS__))

#define CAT(a, ...) PRIMITIVE_CAT(a, __VA_ARGS__)
#define PRIMITIVE_CAT(a, ...) a ## __VA_ARGS__

#define MAX(...) CAT(MAX_,COUNTARGS(__VA_ARGS__))(__VA_ARGS__)

MAX(2,3,4,1)

(2>(3>(4>1?4:1)?3:(4>1?4:1))?2:(3>(4>1?4:1)?3:(4>1?4:1)))

#include <vector>
#include <algorithm>

#define MAX(...) [](auto v)constexpr{
        return *std::max_element(v.begin(),
                                v.end());
    }(std::vector<float>{__VA_ARGS__})