foo.cc: In function 'bool find(int, int, std::string)':
foo.cc:26:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   26 |         for (int i=0;i<b.size()-a.size()+1;i++) {
      |                      ~^~~~~~~~~~~~~~~~~~~~
foo.cc:28:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   28 |                 for (int j=0;j<a.size();j++) {
      |                              ~^~~~~~~~~
foo.cc: In function 'std::string replace(std::string&, int, int, int)':
foo.cc:49:25: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   49 |         for (int i=c+1;i<s.size();i++) s2+=s[i];
      |                        ~^~~~~~~~~
foo.cc: In function 'std::string find_Cs(std::string&, int)':
foo.cc:54:25: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   54 |         for (int i=pos;i<s.size();i++) {
      |                        ~^~~~~~~~~
foo.cc: In function 'bool work(std::string)':
foo.cc:73:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   73 |         for (int i=0;i<s.size();i++) {
      |                      ~^~~~~~~~~
foo.cc:112:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  112 |         for (int k=first_pos;k<s.size();k++) {
      |                              ~^~~~~~~~~
foo.cc:115:41: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  115 |                         for (int i=k+1;i<s.size();i++) {
      |                                        ~^~~~~~~~~
foo.cc:120:46: warning: unused variable 'f' [-Wunused-variable]
  120 |                                         bool f=0;
      |                                              ^
foo.cc: In function 'int main()':
foo.cc:135:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  135 |     for (int i=0;i<S.size();i++) {
      |                  ~^~~~~~~~~
foo.cc:136:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  136 |         for (int j=1;i+j-1<S.size();j++) {
      |                      ~~~~~^~~~~~~~~

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