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:11:1: error: expected primary-expression before '?' token
   11 | ???std::cout<<a+b;
      | ^
a.cc:11:2: error: expected primary-expression before '?' token
   11 | ???std::cout<<a+b;
      |  ^
a.cc:11:3: error: expected primary-expression before '?' token
   11 | ???std::cout<<a+b;
      |   ^
a.cc:11:18: error: expected ':' before ';' token
   11 | ???std::cout<<a+b;
      |                  ^
      |                  :
a.cc:11:18: error: expected primary-expression before ';' token
a.cc:11:18: error: expected ':' before ';' token
   11 | ???std::cout<<a+b;
      |                  ^
      |                  :
a.cc:11:18: error: expected primary-expression before ';' token
a.cc:11:18: error: expected ':' before ';' token
   11 | ???std::cout<<a+b;
      |                  ^
      |                  :
a.cc:11:18: error: expected primary-expression before ';' token
a.cc:13:1: error: expected primary-expression before '?' token
   13 | ???std::cout<<a-b;
      | ^
a.cc:13:2: error: expected primary-expression before '?' token
   13 | ???std::cout<<a-b;
      |  ^
a.cc:13:3: error: expected primary-expression before '?' token
   13 | ???std::cout<<a-b;
      |   ^
a.cc:13:18: error: expected ':' before ';' token
   13 | ???std::cout<<a-b;
      |                  ^
      |                  :
a.cc:13:18: error: expected primary-expression before ';' token
a.cc:13:18: error: expected ':' before ';' token
   13 | ???std::cout<<a-b;
      |                  ^
      |                  :
a.cc:13:18: error: expected primary-expression before ';' token
a.cc:13:18: error: expected ':' before ';' token
   13 | ???std::cout<<a-b;
      |                  ^
      |                  :
a.cc:13:18: error: expected primary-expression before ';' token
a.cc:15:1: error: expected primary-expression before '?' token
   15 | ???std::cout<<a*b;
      | ^
a.cc:15:2: error: expected primary-expression before '?' token
   15 | ???std::cout<<a*b;
      |  ^
a.cc:15:3: error: expected primary-expression before '?' token
   15 | ???std::cout<<a*b;
      |   ^
a.cc:15:18: error: expected ':' before ';' token
   15 | ???std::cout<<a*b;
      |                  ^
      |                  :
a.cc:15:18: error: expected primary-expression before ';' token
a.cc:15:18: error: expected ':' before ';' token
   15 | ???std::cout<<a*b;
      |                  ^
      |                  :
a.cc:15:18: error: expected primary-expression before ';' token
a.cc:15:18: error: expected ':' before ';' token
   15 | ???std::cout<<a*b;
      |                  ^
      |                  :
a.cc:15:18: error: expected primary-expression before ';' token
a.cc:17:1: error: expected primary-expression before '?' token
   17 | ???std::cout<<a/b;
      | ^
a.cc:17:2: error: expected primary-expression before '?' token
   17 | ???std::cout<<a/b;
      |  ^
a.cc:17:3: error: expected primary-expression before '?' token
   17 | ???std::cout<<a/b;
      |   ^
a.cc:17:18: error: expected ':' before ';' token
   17 | ???std::cout<<a/b;
      |                  ^
      |                  :
a.cc:17:18: error: expected primary-expression before ';' token
a.cc:17:18: error: expected ':' before ';' token
   17 | ???std::cout<<a/b;
      |                  ^
      |                  :
a.cc:17:18: error: expected primary-expression before ';' token
a.cc:17:18: error: expected ':' before ';' token
   17 | ???std::cout<<a/b;
      |                  ^
      |                  :
a.cc:17:18: error: expected primary-expression before ';' token
a.cc:19:1: error: expected primary-expression before '?' token
   19 | ???break;
      | ^
a.cc:19:2: error: expected primary-expression before '?' token
   19 | ???break;
      |  ^
a.cc:19:3: error: expected primary-expression before '?' token
   19 | ???break;
      |   ^
a.cc:19:4: error: expected primary-expression before 'break'
   19 | ???break;
      |    ^~~~~
a.cc:19:4: error: expected ':' before 'break'
   19 | ???break;
      |    ^~~~~
      |    :
a.cc:19:4: error: expected primary-expression before 'break'
   19 | ???break;
      |    ^~~~~
a.cc:19:4: error: expected ':' before 'break'
   19 | ???break;
      |    ^~~~~
      |    :
a.cc:19:4: error: expected primary-expression before 'break'
   19 | ???break;
      |    ^~~~~
a.cc:19:4: error: expected ':' before 'break'
   19 | ???break;
      |    ^~~~~
      |    :
a.cc:19:4: error: expected primary-expression before 'break'
   19 | ???break;
      |    ^~~~~