foo.cc: In function 'int main()':
foo.cc:9:14: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
    9 |   if(!(k>='a'&&k<='z'||k>='A'&&k<='Z'))
      |        ~~~~~~^~~~~~~~
foo.cc:11:15: warning: comparison of integer expressions of different signedness: 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   11 |    if(b.size()>s)s=b.size(),m=b;
      |       ~~~~~~~~^~

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