Language: C++

#include<iostream>
using namespace std;

int main(){
    int h, w;
    while(1){
    cin >> h >> w;
    if( h == 0 || w == 0) break;
    for(int a = 0;a < h; a++){
     for(int b = 0;b < w; b++){
       if(a % 2 == 0){
???????????????if(b % 2 == 0) cout << "#";
          else cout << ".";
      } else{
          if(b % 2 == 0) cout <<".";
          else cout<< "#";
     }
   }
   cout<<endl;
  }
  cout << endl;
 }
  return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:12:1: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      | ^
a.cc:12:2: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |  ^
a.cc:12:3: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |   ^
a.cc:12:4: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |    ^
a.cc:12:5: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |     ^
a.cc:12:6: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |      ^
a.cc:12:7: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |       ^
a.cc:12:8: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |        ^
a.cc:12:9: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |         ^
a.cc:12:10: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |          ^
a.cc:12:11: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |           ^
a.cc:12:12: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |            ^
a.cc:12:13: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |             ^
a.cc:12:14: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |              ^
a.cc:12:15: error: expected primary-expression before '?' token
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |               ^
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:12:16: error: expected ':' before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
      |                :
a.cc:12:16: error: expected primary-expression before 'if'
   12 | ???????????????if(b % 2 == 0) cout << "#";
      |                ^~
a.cc:13:11: error: expected '}' before 'else'
   13 |           else cout << ".";
      |           ^~~~
a.cc:11:22: note: to match this '{'
   11 |        if(a % 2 == 0){
      |                      ^
a.cc:14:9: error: 'else' without a previous 'if'
   14 |       } else{
      |         ^~~~
a.cc:15:14: error: 'b' was not declared in this scope
   15 |           if(b % 2 == 0) cout <<".";
      |              ^
a.cc: At global scope:
a.cc:23:3: error: expected unqualified-id before 'return'
   23 |   return 0;
      |   ^~~~~~
a.cc:24:1: error: expected declaration before '}' token
   24 | }
      | ^