foo.cc: In function ‘int main()’:
foo.cc:18:35: error: expected ‘;’ before ‘]’ token
   18 |                         a[index]=1];
      |                                   ^
      |                                   ;
foo.cc:9:23: warning: unused variable ‘index’ [-Wunused-variable]
    9 |         int cnt=0;int index;
      |                       ^~~~~