Language: C++

#include <iostream>

int main() {
    int a, b, n = 0;
    std::cin >> a >> b;
    while (a????????????0 && b != 0) {
        for (int i = a, i <= b, ++i) {
            if (i % 400 == 0) {
                std::cout << i << std::endl;
                n += 1;
            } else if (i % 100 != 0 && i % 4 == 0) {
                std::cout << i << std::endl;
                n += 1;
            } else  {
                continue;
            }
        }
        if (n == 0) {
            std::cout << "NA" << std::endl;
        }
        std::cin >> a >> b;
    }
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:6:14: error: expected primary-expression before '?' token
    6 |     while (a????????????0 && b != 0) {
      |              ^
a.cc:6:15: error: expected primary-expression before '?' token
    6 |     while (a????????????0 && b != 0) {
      |               ^
a.cc:6:16: error: expected primary-expression before '?' token
    6 |     while (a????????????0 && b != 0) {
      |                ^
a.cc:6:17: error: expected primary-expression before '?' token
    6 |     while (a????????????0 && b != 0) {
      |                 ^
a.cc:6:18: error: expected primary-expression before '?' token
    6 |     while (a????????????0 && b != 0) {
      |                  ^
a.cc:6:19: error: expected primary-expression before '?' token
    6 |     while (a????????????0 && b != 0) {
      |                   ^
a.cc:6:20: error: expected primary-expression before '?' token
    6 |     while (a????????????0 && b != 0) {
      |                    ^
a.cc:6:21: error: expected primary-expression before '?' token
    6 |     while (a????????????0 && b != 0) {
      |                     ^
a.cc:6:22: error: expected primary-expression before '?' token
    6 |     while (a????????????0 && b != 0) {
      |                      ^
a.cc:6:23: error: expected primary-expression before '?' token
    6 |     while (a????????????0 && b != 0) {
      |                       ^
a.cc:6:24: error: expected primary-expression before '?' token
    6 |     while (a????????????0 && b != 0) {
      |                        ^
a.cc:6:36: error: expected ':' before ')' token
    6 |     while (a????????????0 && b != 0) {
      |                                    ^
      |                                    :
a.cc:6:36: error: expected primary-expression before ')' token
a.cc:6:36: error: expected ':' before ')' token
    6 |     while (a????????????0 && b != 0) {
      |                                    ^
      |                                    :
a.cc:6:36: error: expected primary-expression before ')' token
a.cc:6:36: error: expected ':' before ')' token
    6 |     while (a????????????0 && b != 0) {
      |                                    ^
      |                                    :
a.cc:6:36: error: expected primary-expression before ')' token
a.cc:6:36: error: expected ':' before ')' token
    6 |     while (a????????????0 && b != 0) {
      |                                    ^
      |                                    :
a.cc:6:36: error: expected primary-expression before ')' token
a.cc:6:36: error: expected ':' before ')' token
    6 |     while (a????????????0 && b != 0) {
      |                                    ^
      |                                    :
a.cc:6:36: error: expected primary-expression before ')' token
a.cc:6:36: error: expected ':' before ')' token
    6 |     while (a????????????0 && b != 0) {
      |                                    ^
      |                                    :
a.cc:6:36: error: expected primary-expression before ')' token
a.cc:6:36: error: expected ':' before ')' token
    6 |     while (a????????????0 && b != 0) {
      |                                    ^
      |                                    :
a.cc:6:36: error: expected primary-expression before ')' token
a.cc:6:36: error: expected ':' before ')' token
    6 |     while (a????????????0 && b != 0) {
      |                                    ^
      |                                    :
a.cc:6:36: error: expected primary-expression before ')' token
a.cc:6:36: error: expected ':' before ')' token
    6 |     while (a????????????0 && b != 0) {
      |                                    ^
      |                                    :
a.cc:6:36: error: expected primary-expression before ')' token
a.cc:6:36: error: expected ':' before ')' token
    6 |     while (a????????????0 && b != 0) {
      |                                    ^
      |                                    :
a.cc:6:36: error: expected primary-expression before ')' token
a.cc:6:36: error: expected ':' before ')' token
    6 |     while (a????????????0 && b != 0) {
      |                                    ^
      |                                    :
a.cc:6:36: error: expected primary-expression before ')' token
a.cc:6:36: error: expected ':' before ')' token
    6 |     while (a????????????0 && b != 0) {
      |                                    ^
      |                                    :
a.cc:6:36: error: expected primary-expression before ')' token
a.cc:7:26: error: expected ';' before '<=' token
    7 |         for (int i = a, i <= b, ++i) {
      |                          ^~~
      |                          ;
a.cc:7:27: error: expected primary-expression before '<=' token
    7 |         for (int i = a, i <= b, ++i) {
      |                           ^~
a.cc:7:36: error: expected ';' before ')' token
    7 |         for (int i = a, i <= b, ++i) {
      |                                    ^
      |                                    ;