foo.cc: In function 'int main()':
foo.cc:9:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (i=0;i<=str1.length()-str2.length();i++)
           ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:14:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (j=0;j<=str2.length()-1;j++)
            ~^~~~~~~~~~~~~~~~~

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