Language: C++

#include <iostream>
using namespace std;

int main ()
{

	int a, b;
	cin >> a >> b;
	if( a < b ){
		cout << "a < b" << endl;
}
    else if ( a > b ){
    	cout << "a > b " << endl;
}
?????????else if ( a == b ){
	    cout << "a == b" << endl;
}
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:15:1: error: expected primary-expression before '?' token
   15 | ?????????else if ( a == b ){
      | ^
a.cc:15:2: error: expected primary-expression before '?' token
   15 | ?????????else if ( a == b ){
      |  ^
a.cc:15:3: error: expected primary-expression before '?' token
   15 | ?????????else if ( a == b ){
      |   ^
a.cc:15:4: error: expected primary-expression before '?' token
   15 | ?????????else if ( a == b ){
      |    ^
a.cc:15:5: error: expected primary-expression before '?' token
   15 | ?????????else if ( a == b ){
      |     ^
a.cc:15:6: error: expected primary-expression before '?' token
   15 | ?????????else if ( a == b ){
      |      ^
a.cc:15:7: error: expected primary-expression before '?' token
   15 | ?????????else if ( a == b ){
      |       ^
a.cc:15:8: error: expected primary-expression before '?' token
   15 | ?????????else if ( a == b ){
      |        ^
a.cc:15:9: error: expected primary-expression before '?' token
   15 | ?????????else if ( a == b ){
      |         ^
a.cc:15:10: error: expected primary-expression before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
a.cc:15:10: error: expected ':' before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
      |          :
a.cc:15:10: error: expected primary-expression before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
a.cc:15:10: error: expected ':' before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
      |          :
a.cc:15:10: error: expected primary-expression before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
a.cc:15:10: error: expected ':' before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
      |          :
a.cc:15:10: error: expected primary-expression before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
a.cc:15:10: error: expected ':' before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
      |          :
a.cc:15:10: error: expected primary-expression before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
a.cc:15:10: error: expected ':' before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
      |          :
a.cc:15:10: error: expected primary-expression before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
a.cc:15:10: error: expected ':' before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
      |          :
a.cc:15:10: error: expected primary-expression before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
a.cc:15:10: error: expected ':' before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
      |          :
a.cc:15:10: error: expected primary-expression before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
a.cc:15:10: error: expected ':' before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
      |          :
a.cc:15:10: error: expected primary-expression before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
a.cc:15:10: error: expected ':' before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~
      |          :
a.cc:15:10: error: expected primary-expression before 'else'
   15 | ?????????else if ( a == b ){
      |          ^~~~