foo.cc: In function 'int main()':
foo.cc:8:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<str.size();i++)
              ~^~~~~~~~~~~
foo.cc:11:10: error: no 'operator++(int)' declared for postfix '++' [-fpermissive]
       cnt++;
       ~~~^~

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