Language: C++

#include <iostream>
using namespace std;
 
int main() {
	int a,b;
	char op;
	while(true){
		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;
	}
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:9:23: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
    9 |                 if(op == "?") break???
      |                    ~~~^~~~~~
a.cc:9:36: error: expected ';' before '?' token
    9 |                 if(op == "?") break???
      |                                    ^
      |                                    ;
a.cc:9:36: error: expected primary-expression before '?' token
a.cc:9:37: error: expected primary-expression before '?' token
    9 |                 if(op == "?") break???
      |                                     ^
a.cc:9:38: error: expected primary-expression before '?' token
    9 |                 if(op == "?") break???
      |                                      ^
a.cc:10:17: error: expected primary-expression before 'else'
   10 |                 else if(op == "+") cout << a+b << endl;
      |                 ^~~~
a.cc:9:39: error: expected ':' before 'else'
    9 |                 if(op == "?") break???
      |                                       ^
      |                                       :
   10 |                 else if(op == "+") cout << a+b << endl;
      |                 ~~~~                   
a.cc:10:17: error: expected primary-expression before 'else'
   10 |                 else if(op == "+") cout << a+b << endl;
      |                 ^~~~
a.cc:9:39: error: expected ':' before 'else'
    9 |                 if(op == "?") break???
      |                                       ^
      |                                       :
   10 |                 else if(op == "+") cout << a+b << endl;
      |                 ~~~~                   
a.cc:10:17: error: expected primary-expression before 'else'
   10 |                 else if(op == "+") cout << a+b << endl;
      |                 ^~~~
a.cc:9:39: error: expected ':' before 'else'
    9 |                 if(op == "?") break???
      |                                       ^
      |                                       :
   10 |                 else if(op == "+") cout << a+b << endl;
      |                 ~~~~                   
a.cc:10:17: error: expected primary-expression before 'else'
   10 |                 else if(op == "+") cout << a+b << endl;
      |                 ^~~~
a.cc:11:17: error: 'else' without a previous 'if'
   11 |                 else if(op == "-") cout << a-b << endl;
      |                 ^~~~
a.cc:11:28: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   11 |                 else if(op == "-") cout << a-b << endl;
      |                         ~~~^~~~~~
a.cc:12:28: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   12 |                 else if(op == "/") cout << a/b << endl;
      |                         ~~~^~~~~~
a.cc:13:28: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   13 |                 else if(op == "*") cout << a*b << endl;
      |                         ~~~^~~~~~