variable ambiguous abbreviation r(111)

[Donghan Su]

Hi,
I have 65 variables in my data set names dtia1, dtia2..dtia65. I wish to replace the contents(replace letter string in those variable with a number)in those variables using loop.
Then I kept getting the dtia ambiguous abbreviation r(111) error and do not know where does it come from.

[Fei Wang]

The first is not right, and the second is correct.

dtia'i'
dtia`i'