Language: C++

#include<iostream>

int main(){
  int a, b;
  char op;
  while (true){
    cin >> a >> op >> b;
    if (op == "?") break;
    if (op == "+") cout << a+b << endl;
    if (op == "-") cout << a-b << endl;
    if (op == "*") cout << a*b << endl;
    if (op == "/") cout << a/b << endl;
  }
  return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:7:5: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    7 |     cin >> a >> op >> b;
      |     ^~~
      |     std::cin
In file included 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:8:12: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
    8 |     if (op == "?") break;
      |         ~~~^~~~~~
a.cc:9:12: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
    9 |     if (op == "+") cout << a+b << endl;
      |         ~~~^~~~~~
a.cc:9:20: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    9 |     if (op == "+") cout << a+b << endl;
      |                    ^~~~
      |                    std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:9:35: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
    9 |     if (op == "+") cout << a+b << endl;
      |                                   ^~~~
      |                                   std::endl
In file included from /usr/include/c++/14/iostream:41:
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:10:12: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   10 |     if (op == "-") cout << a-b << endl;
      |         ~~~^~~~~~
a.cc:10:20: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   10 |     if (op == "-") cout << a-b << endl;
      |                    ^~~~
      |                    std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:10:35: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   10 |     if (op == "-") cout << a-b << endl;
      |                                   ^~~~
      |                                   std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:11:12: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   11 |     if (op == "*") cout << a*b << endl;
      |         ~~~^~~~~~
a.cc:11:20: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   11 |     if (op == "*") cout << a*b << endl;
      |                    ^~~~
      |                    std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:11:35: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   11 |     if (op == "*") cout << a*b << endl;
      |                                   ^~~~
      |                                   std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:12:12: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   12 |     if (op == "/") cout << a/b << endl;
      |         ~~~^~~~~~
a.cc:12:20: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   12 |     if (op == "/") cout << a/b << endl;
      |                    ^~~~
      |                    std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:12:35: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   12 |     if (op == "/") cout << a/b << endl;
      |                                   ^~~~
      |                                   std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~