Language: C++

#include<iostream>
int main(){
    int a,b;
    char op;
    while(1){
        cin>>a>>op>>b;
        if(op=="?")break;
        else if(op=="+")cout<<a+b<<endl;
        else if(op=="-")cout<<a-b<<endl;
        else if(op=="*")cout<<a*b<<endl;
        else if(op=="/")cout<<a/b<<endl;
    }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:6:9: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    6 |         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:7:14: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
    7 |         if(op=="?")break;
      |            ~~^~~~~
a.cc:8:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
    8 |         else if(op=="+")cout<<a+b<<endl;
      |                 ~~^~~~~
a.cc:8:25: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    8 |         else 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:8:36: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
    8 |         else 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:9:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
    9 |         else if(op=="-")cout<<a-b<<endl;
      |                 ~~^~~~~
a.cc:9:25: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    9 |         else 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:9:36: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
    9 |         else 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:10:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   10 |         else if(op=="*")cout<<a*b<<endl;
      |                 ~~^~~~~
a.cc:10:25: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   10 |         else 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:10:36: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   10 |         else 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:11:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   11 |         else if(op=="/")cout<<a/b<<endl;
      |                 ~~^~~~~
a.cc:11:25: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   11 |         else 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:11:36: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   11 |         else 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)
      |     ^~~~