I'm not exactly sure what you mean by two counters? What you have for an example just assigns a 1 to the value rn. RN can only contain a value of 0-9 as you have it. To increment it you'd use rn=rn+"1". If you are meaning two separate counters, you'd have to define two variables:
rn(1,.0)=rn+"1"
co(10,.0)=co+"1"