/in/foo.cc: In function 'int dfs(int, int, int)':
/in/foo.cc:21:3: error: return-statement with no value, in function returning 'int' [-fpermissive]
   return;
   ^~~~~~
/in/foo.cc:23:17: warning: operation on 'cnt' may be undefined [-Wsequence-point]
  dfs(x+a[cnt],y,++cnt);
                 ^~~~~
/in/foo.cc:24:17: warning: operation on 'cnt' may be undefined [-Wsequence-point]
  dfs(x+a[cnt],y,++cnt);
                 ^~~~~