Main.cc: In function ‘int main()’: Main.cc:7:2: error: ‘strlwr’ was not declared in this scope strlwr(a); ^~~~~~ Main.cc:7:2: note: suggested alternative: ‘strstr’ strlwr(a); ^~~~~~ strstr Main.cc:10:33: error: cannot convert ‘std::__cxx11::string {aka std::__cxx11::basic_string}’ to ‘const char*’ for argument ‘1’ to ‘size_t strlen(const char*)’ for(int i = 0; i < min(strlen(a), strlen(b)); i++){ ^ Main.cc:10:44: error: cannot convert ‘std::__cxx11::string {aka std::__cxx11::basic_string}’ to ‘const char*’ for argument ‘1’ to ‘size_t strlen(const char*)’ for(int i = 0; i < min(strlen(a), strlen(b)); i++){ ^