Does not exist strupr() and strlwr() in the library <string.h> of c++?

Answer 1

That's because strupr() and strlwr() are not standard function, these functions are sometimes shipped with the implementation of the compiler on some platforms but generally it is recomemded to write your own custom functions to conver the string to upper and/or lower case (you can use toupper() and tolower() from <ctype.h> header for the same)

Answer 2

By the way, when using C header files in C++, you should include <cstring> instead of <string.h>
(c prefix instead of .h suffix)