foo.cc: In function 'int main()':
foo.cc:9:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    9 |  for(int i=0;i<str.size();i++)
      |              ~^~~~~~~~~~~
foo.cc:16:13: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   16 |    if(u=='('&&t!=')'||u=='['&&t!=']')
      |       ~~~~~~^~~~~~~~

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