Language: C++

#include <iostream>
using namespace std;

int main()
{
char op;
int a,b,i;


for(i=0;cin >> a >> op >> b && op == ?;i++)
{
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:10:38: error: expected primary-expression before '?' token
   10 | for(i=0;cin >> a >> op >> b && op == ?;i++)
      |                                      ^
a.cc:10:39: error: expected primary-expression before ';' token
   10 | for(i=0;cin >> a >> op >> b && op == ?;i++)
      |                                       ^
a.cc:10:39: error: expected ':' before ';' token
   10 | for(i=0;cin >> a >> op >> b && op == ?;i++)
      |                                       ^
      |                                       :
a.cc:10:39: error: expected primary-expression before ';' token
a.cc:13:1: error: expected primary-expression before '?' token
   13 | ???cout << a+b << endl;
      | ^
a.cc:13:2: error: expected primary-expression before '?' token
   13 | ???cout << a+b << endl;
      |  ^
a.cc:13:3: error: expected primary-expression before '?' token
   13 | ???cout << a+b << endl;
      |   ^
a.cc:13:23: error: expected ':' before ';' token
   13 | ???cout << a+b << endl;
      |                       ^
      |                       :
a.cc:13:23: error: expected primary-expression before ';' token
a.cc:13:23: error: expected ':' before ';' token
   13 | ???cout << a+b << endl;
      |                       ^
      |                       :
a.cc:13:23: error: expected primary-expression before ';' token
a.cc:13:23: error: expected ':' before ';' token
   13 | ???cout << a+b << endl;
      |                       ^
      |                       :
a.cc:13:23: error: expected primary-expression before ';' token
a.cc:15:1: error: expected primary-expression before '?' token
   15 | ???cout << a-b << endl;
      | ^
a.cc:15:2: error: expected primary-expression before '?' token
   15 | ???cout << a-b << endl;
      |  ^
a.cc:15:3: error: expected primary-expression before '?' token
   15 | ???cout << a-b << endl;
      |   ^
a.cc:15:23: error: expected ':' before ';' token
   15 | ???cout << a-b << endl;
      |                       ^
      |                       :
a.cc:15:23: error: expected primary-expression before ';' token
a.cc:15:23: error: expected ':' before ';' token
   15 | ???cout << a-b << endl;
      |                       ^
      |                       :
a.cc:15:23: error: expected primary-expression before ';' token
a.cc:15:23: error: expected ':' before ';' token
   15 | ???cout << a-b << endl;
      |                       ^
      |                       :
a.cc:15:23: error: expected primary-expression before ';' token
a.cc:17:1: error: expected primary-expression before '?' token
   17 | ???cout << a*b << endl;
      | ^
a.cc:17:2: error: expected primary-expression before '?' token
   17 | ???cout << a*b << endl;
      |  ^
a.cc:17:3: error: expected primary-expression before '?' token
   17 | ???cout << a*b << endl;
      |   ^
a.cc:17:23: error: expected ':' before ';' token
   17 | ???cout << a*b << endl;
      |                       ^
      |                       :
a.cc:17:23: error: expected primary-expression before ';' token
a.cc:17:23: error: expected ':' before ';' token
   17 | ???cout << a*b << endl;
      |                       ^
      |                       :
a.cc:17:23: error: expected primary-expression before ';' token
a.cc:17:23: error: expected ':' before ';' token
   17 | ???cout << a*b << endl;
      |                       ^
      |                       :
a.cc:17:23: error: expected primary-expression before ';' token
a.cc:19:1: error: expected primary-expression before '?' token
   19 | ???cout << a/b << endl;
      | ^
a.cc:19:2: error: expected primary-expression before '?' token
   19 | ???cout << a/b << endl;
      |  ^
a.cc:19:3: error: expected primary-expression before '?' token
   19 | ???cout << a/b << endl;
      |   ^
a.cc:19:23: error: expected ':' before ';' token
   19 | ???cout << a/b << endl;
      |                       ^
      |                       :
a.cc:19:23: error: expected primary-expression before ';' token
a.cc:19:23: error: expected ':' before ';' token
   19 | ???cout << a/b << endl;
      |                       ^
      |                       :
a.cc:19:23: error: expected primary-expression before ';' token
a.cc:19:23: error: expected ':' before ';' token
   19 | ???cout << a/b << endl;
      |                       ^
      |                       :
a.cc:19:23: error: expected primary-expression before ';' token
a.cc:22:2: error: expected '}' at end of input
   22 | }
      |  ^
a.cc:5:1: note: to match this '{'
    5 | {
      | ^