foo.cc: In function 'void compare(int, int)':
foo.cc:14:40: warning: left operand of comma operator has no effect [-Wunused-value]
  for (char c1 = str[a], c2 = str[b]; a < tempa + n, b < tempb + n; a ++, b ++ , c1 = str[a], c2 = str[b])
                                      ~~^~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:31:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%s", str);
  ~~~~~^~~~~~~~~~~

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