outside of a struct, password is the best way IMHO.
username also works but its silly to do that to yourself.
you can also use a pointer:
char * foo = "foo";
(I know you said no pointer but c-strings don't require memory allocation/destruction via special syntax / parsing of the syntax). I do not like the * approach either, but without the memory management its unlike other pointer efforts.
I am not sure you can set the values in the type. And, you need to be careful; if you plan to change the username or password later, what if they put in a 10 character password? You only created space for 4 chars this way. I am out of practice at C but I think you need to give bigger [size]s for these and find another way to initialize them. Consider: http://www.c4learn.com/c-programming/c-initializing-structure/