foo.cc: In function 'int main()':
foo.cc:43:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < strlen(n); i ++ )
                  ~~^~~~~~~~~~~
foo.cc:39:3: warning: 'a' may be used uninitialized in this function [-Wmaybe-uninitialized]
   if (a != b) add(a, b);
   ^~
foo.cc:39:3: warning: 'b' may be used uninitialized in this function [-Wmaybe-uninitialized]

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