/in/foo.cc: In function 'int main(int, const char**)':
/in/foo.cc:16:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<strlen(a);i++)
                  ^
/in/foo.cc:23:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<strlen(b);i++)
                  ^
/in/foo.cc:30:18: error: cannot convert 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' to 'const char*' for argument '1' to 'int strcmp(const char*, const char*)'
     if(strcmp(c,d)==0)
                  ^