How to using variable on looping mssql

I have some varchar variable like this:

@var1='data a', 
@var2='data b',
@var3='data c', 
...,
@varn='data n'

i want to insert these variable on looping script.

DECLARE @counter INT
SET @counter = 1
WHILE(@counter <= n)
BEGIN
update [table] set [header] where data=[@var1-n]
set @counter=@counter+1
END
GO

how to make @var1 - @varn can use with loop on [@var1-n]?