Main.cc: In function ‘int main()’: Main.cc:9:2: error: ‘strlwr’ was not declared in this scope strlwr(a); ^~~~~~ Main.cc:9:2: note: suggested alternative: ‘strstr’ strlwr(a); ^~~~~~ strstr Main.cc:11:15: error: cannot convert ‘std::__cxx11::string {aka std::__cxx11::basic_string}’ to ‘const char*’ for argument ‘1’ to ‘int strcmp(const char*, const char*)’ if(strcmp(a,b)==0) cout<<"="; ^ Main.cc:12:20: error: cannot convert ‘std::__cxx11::string {aka std::__cxx11::basic_string}’ to ‘const char*’ for argument ‘1’ to ‘int strcmp(const char*, const char*)’ else if(strcmp(a,b)<0) cout<<"<" ; ^