Language: C++

#include <iostream>
int main(){
int a,b;
char op;

while(1){

std::cin>>a>>op>>b;
if(op == '?'){
break;
} else if(op == '+'){
???std::cout<<a+b;
} else if(op == '-'){
???std::cout<<a-b;
} else if( op == '*'){
???std::cout<<a*b;
} else if(op == '/'){
???std::cout<<a/b;
} else {
???break;
}

}

return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:12:1: error: expected primary-expression before '?' token
   12 | ???std::cout<<a+b;
      | ^
a.cc:12:2: error: expected primary-expression before '?' token
   12 | ???std::cout<<a+b;
      |  ^
a.cc:12:3: error: expected primary-expression before '?' token
   12 | ???std::cout<<a+b;
      |   ^
a.cc:12:18: error: expected ':' before ';' token
   12 | ???std::cout<<a+b;
      |                  ^
      |                  :
a.cc:12:18: error: expected primary-expression before ';' token
a.cc:12:18: error: expected ':' before ';' token
   12 | ???std::cout<<a+b;
      |                  ^
      |                  :
a.cc:12:18: error: expected primary-expression before ';' token
a.cc:12:18: error: expected ':' before ';' token
   12 | ???std::cout<<a+b;
      |                  ^
      |                  :
a.cc:12:18: error: expected primary-expression before ';' token
a.cc:14:1: error: expected primary-expression before '?' token
   14 | ???std::cout<<a-b;
      | ^
a.cc:14:2: error: expected primary-expression before '?' token
   14 | ???std::cout<<a-b;
      |  ^
a.cc:14:3: error: expected primary-expression before '?' token
   14 | ???std::cout<<a-b;
      |   ^
a.cc:14:18: error: expected ':' before ';' token
   14 | ???std::cout<<a-b;
      |                  ^
      |                  :
a.cc:14:18: error: expected primary-expression before ';' token
a.cc:14:18: error: expected ':' before ';' token
   14 | ???std::cout<<a-b;
      |                  ^
      |                  :
a.cc:14:18: error: expected primary-expression before ';' token
a.cc:14:18: error: expected ':' before ';' token
   14 | ???std::cout<<a-b;
      |                  ^
      |                  :
a.cc:14:18: error: expected primary-expression before ';' token
a.cc:16:1: error: expected primary-expression before '?' token
   16 | ???std::cout<<a*b;
      | ^
a.cc:16:2: error: expected primary-expression before '?' token
   16 | ???std::cout<<a*b;
      |  ^
a.cc:16:3: error: expected primary-expression before '?' token
   16 | ???std::cout<<a*b;
      |   ^
a.cc:16:18: error: expected ':' before ';' token
   16 | ???std::cout<<a*b;
      |                  ^
      |                  :
a.cc:16:18: error: expected primary-expression before ';' token
a.cc:16:18: error: expected ':' before ';' token
   16 | ???std::cout<<a*b;
      |                  ^
      |                  :
a.cc:16:18: error: expected primary-expression before ';' token
a.cc:16:18: error: expected ':' before ';' token
   16 | ???std::cout<<a*b;
      |                  ^
      |                  :
a.cc:16:18: error: expected primary-expression before ';' token
a.cc:18:1: error: expected primary-expression before '?' token
   18 | ???std::cout<<a/b;
      | ^
a.cc:18:2: error: expected primary-expression before '?' token
   18 | ???std::cout<<a/b;
      |  ^
a.cc:18:3: error: expected primary-expression before '?' token
   18 | ???std::cout<<a/b;
      |   ^
a.cc:18:18: error: expected ':' before ';' token
   18 | ???std::cout<<a/b;
      |                  ^
      |                  :
a.cc:18:18: error: expected primary-expression before ';' token
a.cc:18:18: error: expected ':' before ';' token
   18 | ???std::cout<<a/b;
      |                  ^
      |                  :
a.cc:18:18: error: expected primary-expression before ';' token
a.cc:18:18: error: expected ':' before ';' token
   18 | ???std::cout<<a/b;
      |                  ^
      |                  :
a.cc:18:18: error: expected primary-expression before ';' token
a.cc:20:1: error: expected primary-expression before '?' token
   20 | ???break;
      | ^
a.cc:20:2: error: expected primary-expression before '?' token
   20 | ???break;
      |  ^
a.cc:20:3: error: expected primary-expression before '?' token
   20 | ???break;
      |   ^
a.cc:20:4: error: expected primary-expression before 'break'
   20 | ???break;
      |    ^~~~~
a.cc:20:4: error: expected ':' before 'break'
   20 | ???break;
      |    ^~~~~
      |    :
a.cc:20:4: error: expected primary-expression before 'break'
   20 | ???break;
      |    ^~~~~
a.cc:20:4: error: expected ':' before 'break'
   20 | ???break;
      |    ^~~~~
      |    :
a.cc:20:4: error: expected primary-expression before 'break'
   20 | ???break;
      |    ^~~~~
a.cc:20:4: error: expected ':' before 'break'
   20 | ???break;
      |    ^~~~~
      |    :
a.cc:20:4: error: expected primary-expression before 'break'
   20 | ???break;
      |    ^~~~~