foo.cc: In function 'void change_lowercase(std::__cxx11::string&)':
foo.cc:10:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i < s.size(); i++)
                 ~~^~~~~~~~~~
foo.cc: In function 'void cutpair(std::__cxx11::string, std::vector<codepair>&)':
foo.cc:30:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while(s[i] == ' ' && i < s.size()) cout << ' ', ++i;
                       ~~^~~~~~~~~~
foo.cc:31:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while(i < s.size()) {
        ~~^~~~~~~~~~
foo.cc: In function 'void putdecode(codepair)':
foo.cc:56:32: warning: array subscript has type 'char' [-Wchar-subscripts]
  pair<int, int> a = mapcode[p.f];
                                ^
foo.cc:57:32: warning: array subscript has type 'char' [-Wchar-subscripts]
  pair<int, int> b = mapcode[p.r];
                                ^
foo.cc: In function 'int main()':
foo.cc:91:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i < k.size(); i++) {
                 ~~^~~~~~~~~~
foo.cc:93:19: warning: array subscript has type 'char' [-Wchar-subscripts]
   else if(uni[k[i]]) continue;
                   ^
foo.cc:96:12: warning: array subscript has type 'char' [-Wchar-subscripts]
    uni[k[i]] = true, mapcode[k[i]] = make_pair(p, q);
            ^
foo.cc:96:34: warning: array subscript has type 'char' [-Wchar-subscripts]
    uni[k[i]] = true, mapcode[k[i]] = make_pair(p, q);
                                  ^
foo.cc:128:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i < v.size(); i++) {
                 ~~^~~~~~~~~~

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