In the astrobasic help, look at 'pointers'.
Yes, the name of the font should be in 's'.
command() only accepts integers, numeric. But using pointers enables one to use other types by giving not the variable, but the address of the variable. This is a concept from c/c++ and assembly, pointers are very common there. You already used them in memval() where you have a pointer to the structure from memget().
It is a difficult subject to get your head around at first, but it is very powerful.
In this case it enables me to use command() for other things besides integers.
ps I noticed an error in above example, correct syntax is
command(TEXT, x, 17, &s)
x is the number of the text control.