foo.cc: In member function 'bool kuo_hao::place()':
foo.cc:29:8: warning: statement has no effect [-Wunused-value]
   29 |   for (i1; a[i1] != '('; i1++);
      |        ^~
foo.cc:30:8: warning: statement has no effect [-Wunused-value]
   30 |   for (i2; a[i2] != ')'; i2++);
      |        ^~
foo.cc:31:8: warning: statement has no effect [-Wunused-value]
   31 |   for (l1; a[l1] != '['; l1++);
      |        ^~
foo.cc:32:8: warning: statement has no effect [-Wunused-value]
   32 |   for (l2; a[l2] != ']'; l2++);
      |        ^~
foo.cc: In function 'int main()':
foo.cc:51:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   51 |  for (int i = 0; i < a.length(); i++)
      |                  ~~^~~~~~~~~~~~

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