Language: C++

#include <bits/stdc++.h>
using namepsace std;

int main() {
	int a??, b;
	cin ?? >> a >> b ??;
	cout << a ?? + b << "\n";
	return 0;
}#include <bits/stdc++.h>
using namespace std;

int main() {
	int a??, b;
	cin ?? >> a >> b ??;
	cout << a ?? + b << "\n";
	return 0;
}

Compiler output:
a.cc:9:2: error: stray '#' in program
    9 | }#include <bits/stdc++.h>
      |  ^
a.cc:2:7: error: expected nested-name-specifier before 'namepsace'
    2 | using namepsace std;
      |       ^~~~~~~~~
a.cc: In function 'int main()':
a.cc:5:14: error: expected initializer before '?' token
    5 |         int a??, b;
      |              ^
a.cc:6:9: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    6 |         cin ?? >> a >> b ??;
      |         ^~~
      |         std::cin
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:146,
                 from a.cc:1:
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:6:14: error: expected primary-expression before '?' token
    6 |         cin ?? >> a >> b ??;
      |              ^
a.cc:6:16: error: expected primary-expression before '>>' token
    6 |         cin ?? >> a >> b ??;
      |                ^~
a.cc:6:19: error: 'a' was not declared in this scope
    6 |         cin ?? >> a >> b ??;
      |                   ^
a.cc:6:24: error: 'b' was not declared in this scope
    6 |         cin ?? >> a >> b ??;
      |                        ^
a.cc:6:27: error: expected primary-expression before '?' token
    6 |         cin ?? >> a >> b ??;
      |                           ^
a.cc:6:28: error: expected primary-expression before ';' token
    6 |         cin ?? >> a >> b ??;
      |                            ^
a.cc:6:28: error: expected ':' before ';' token
    6 |         cin ?? >> a >> b ??;
      |                            ^
      |                            :
a.cc:6:28: error: expected primary-expression before ';' token
a.cc:6:28: error: expected ':' before ';' token
    6 |         cin ?? >> a >> b ??;
      |                            ^
      |                            :
a.cc:6:28: error: expected primary-expression before ';' token
a.cc:6:28: error: expected ':' before ';' token
    6 |         cin ?? >> a >> b ??;
      |                            ^
      |                            :
a.cc:6:28: error: expected primary-expression before ';' token
a.cc:6:28: error: expected ':' before ';' token
    6 |         cin ?? >> a >> b ??;
      |                            ^
      |                            :
a.cc:6:28: error: expected primary-expression before ';' token
a.cc:7:9: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    7 |         cout << a ?? + b << "\n";
      |         ^~~~
      |         std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:7:20: error: expected primary-expression before '?' token
    7 |         cout << a ?? + b << "\n";
      |                    ^
a.cc:7:33: error: expected ':' before ';' token
    7 |         cout << a ?? + b << "\n";
      |                                 ^
      |                                 :
a.cc:7:33: error: expected primary-expression before ';' token
a.cc:7:33: error: expected ':' before ';' token
    7 |         cout << a ?? + b << "\n";
      |                                 ^
      |                                 :
a.cc:7:33: error: expected primary-expression before ';' token
a.cc: At global scope:
a.cc:9:3: error: 'include' does not name a type
    9 | }#include <bits/stdc++.h>
      |   ^~~~~~~
a.cc:12:5: error: redefinition of 'int main()'
   12 | int main() {
      |     ^~~~
a.cc:4:5: note: 'int main()' previously defined here
    4 | int main() {
      |     ^~~~
a.cc: In function 'int main()':
a.cc:13:14: error: expected initializer before '?' token
   13 |         int a??, b;
      |              ^
a.cc:14:9: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
   14 |         cin ?? >> a >> b ??;
      |         ^~~
      |         std::cin
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:14:14: error: expected primary-expression before '?' token
   14 |         cin ?? >> a >> b ??;
      |              ^
a.cc:14:16: error: expected primary-expression before '>>' token
   14 |         cin ?? >> a >> b ??;
      |                ^~
a.cc:14:19: error: 'a' was not declared in this scope
   14 |         cin ?? >> a >> b ??;
      |                   ^
a.cc:14:24: error: 'b' was not declared in this scope
   14 |         cin ?? >> a >> b ??;
      |                        ^
a.cc:14:27: error: expected primary-expression before '?' token
   14 |         cin ?? >> a >> b ??;
      |                           ^
a.cc:14:28: error: expected primary-expression before ';' token
   14 |         cin ?? >> a >> b ??;
      |                            ^
a.cc:14:28: error: expected ':' before ';' token
   14 |         cin ?? >> a >> b ??;
      |                            ^
      |                            :
a.cc:14:28: error: expected primary-expression before ';' token
a.cc:14:28: error: expected ':' before ';' token
   14 |         cin ?? >> a >> b ??;
      |                            ^
      |                            :
a.cc:14:28: error: expected primary-expression before ';' token
a.cc:14:28: error: expected ':' before ';' token
   14 |         cin ?? >> a >> b ??;
      |                            ^
      |                            :
a.cc:14:28: error: expected primary-expression before ';' token
a.cc:14:28: error: expected ':' before ';' token
   14 |         cin ?? >> a >> b ??;
      |                            ^
      |                            :
a.cc:14:28: error: expected primary-expression before ';' token
a.cc:15:9: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   15 |         cout << a ?? + b << "\n";
      |         ^~~~
      |         std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:15:20: error: expected primary-expression before '?' token
   15 |         cout << a ?? + b << "\n";
      |                    ^
a.cc:15:33: error: expected ':' before ';' token
   15 |         cout << a ?? + b << "\n";
      |                                 ^
      |                                 :
a.cc:15:33: error: expected primary-expression before ';' token
a.cc:15:33: error: expected ':' before ';' token
   15 |         cout << a ?? + b << "\n";
      |                                 ^
      |                                 :
a.cc:15:33: error: expected primary-expression before ';' token