[R] Incremental operator

[S Peri]

Hi group, 
 I am trying to get the LocusID numbers from my affy
expression matrix.  

I instantiated rownames function to get an object with
all the probe IDs.

> where.affy.at <- rownames(gliexp)

Now I wanted to get another object with the LocusIDs
in it like the following.  However, I get the
following error. How come i = i +1 is not considered
as incrementation here. I know there is some trouble
in defining. I come from Python background so I am
stuck. Could any one help me please. 


>for (i in where.affy.at){
+   gene.locusid.affy <- get(i,env= hgu95av2LOCUSID)
+ i = i + 1
+ gene.locusid.affy
+ }
Error in i + 1 : non-numeric argument to binary
operator


Thank you. 
PS