Sorry, here's the corrected code.
LPARAMETERS curtable, oldtable
LOCAL old,cur,afieldname,afieldtype,afieldsize,zfieldtoadd
old = FCOUNT(oldtable)
cur = FCOUNT(curtable)
SELECT (curtable)
= AFIELDS(aMyStruc, (curtable))
do while old <= cur
old = old + 1
afieldname = aMyStruc(old,1)
afieldtype = aMyStruc(old,2)
afieldsize = aMyStruc(old,3)
zfieldtoadd = afieldname + " " + afieldtype + ;
"(" + LTRIM(STR(afieldsize)) + ")"
SELECT (oldtable)
ALTER TABLE (oldtable) add column (zfieldtoadd)
ENDDO
SELECT (curtable)
INSERT INTO (curtable) SELECT * FROM (oldtable)