foo.cc: In function 'int main()':
foo.cc:13:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0;i<a.length();i++)CS[i][0]=0;
                     ~^~~~~~~~~~~
foo.cc:14:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0;i<b.length();i++)CS[0][i]=0;
                     ~^~~~~~~~~~~
foo.cc:15:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0;i<a.length();i++)
                     ~^~~~~~~~~~~
foo.cc:16:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int j=0;j<b.length();j++)
                     ~^~~~~~~~~~~

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