/in/foo.cc: In function 'int main()':
/in/foo.cc:14:14: warning: NULL used in arithmetic [-Wpointer-arith]
  while(a[i]!=NULL || b[k]!=NULL)
              ^~~~
/in/foo.cc:14:28: warning: NULL used in arithmetic [-Wpointer-arith]
  while(a[i]!=NULL || b[k]!=NULL)
                            ^~~~
/in/foo.cc:29:11: warning: NULL used in arithmetic [-Wpointer-arith]
  if(a[i]==NULL)
           ^~~~
/in/foo.cc:31:15: warning: NULL used in arithmetic [-Wpointer-arith]
   while(b[k]!=NULL)
               ^~~~
/in/foo.cc:38:11: warning: NULL used in arithmetic [-Wpointer-arith]
  if(b[k]==NULL)
           ^~~~
/in/foo.cc:40:15: warning: NULL used in arithmetic [-Wpointer-arith]
   while(a[i]!=NULL)
               ^~~~