Q:

SAS: How can we replace values for bunch of data using loops?

I have been trying to replace bunch of data to different format.
For instance, the variable called Week starts from a value 1124 to a value 1175. I want to change this value starting from 1. 
That is,
Week     Week
1124       1
1125       2

If this was R, I would be using for-loop and store them back to week to replace them, but I am not sure how to formulate something similar in SAS.The only method I got was:
if Week = 1124 then Week = 1;
and so forth.
run;

This is very inefficient as I have to write 30+ times. Are there any efficient method to tackle this issue? In other words, is there something similar to for-loops?

A:

SAS DATA step is an implicit loop -- every row in the data set is processed until there are no more rows.  Use simple arithmetic to transform the value of the week variable.
data want;
  set have;
  week = week - 1123;
run;

