foo.cc: In function 'int main(int, char**)':
foo.cc:12:6: warning: unused variable 'k' [-Wunused-variable]
   12 |  int k=0,cnt=0;
      |      ^
foo.cc:12:10: warning: unused variable 'cnt' [-Wunused-variable]
   12 |  int k=0,cnt=0;
      |          ^~~
foo.cc: In function 'void Replace(std::string&, std::string&, std::string&)':
foo.cc:18:6: warning: unused variable 'slen' [-Wunused-variable]
   18 |  int slen=s.length(), tlen=t.length(), ulen=u.length();
      |      ^~~~
foo.cc:18:23: warning: unused variable 'tlen' [-Wunused-variable]
   18 |  int slen=s.length(), tlen=t.length(), ulen=u.length();
      |                       ^~~~

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