basic php…

i’m not too familiar with php so i was wondering if you could help me with excluding additional categories in this code. first off, the original code was:

query_posts(?showposts=1);

but then to remove category id#3 from being displayed, &cat-3? was added

query_posts(?showposts=1&cat=-3?);

everything worked fine, but then i wanted category id#4 to be removed, so i tried

query_posts(?showposts=1&cat=-3&cat=-4?);

but that didn’t work..

query_posts(?showposts=1&cat=-3&&cat=-4?);

and

query_posts(?showposts=1&cat=-3&&-4?);

do not work either..

can anyone with php knowledge help me with this? i think it’s pretty basic php but i don’t know how to do it >_< thanks in advance!