Need to understand what if/then statement is doing

[alaxman]

I have this piece of code:

if filldates(i)<= start_dt + ii -1 <= filldates(i)+days_supply(i)-1
		then daydummy(ii)=1;
		end;

Can someone help me understand what the IF statement is checking? There doesn't seem to be an AND or an OR operator, but two conditional operators (<=). 

[SASKiwi]

As I understand it, the IF condition is true if (start_dt + ii -1) is between the values of (filldates(i)) and (filldates(i)+days_supply(i)-1).

The lack of brackets in this expression is concerning and would make it easier to read:

if filldates(i) <= (start_dt + ii -1) <= (filldates(i)+days_supply(i)-1)
		then daydummy(ii)=1;
		end;

[alaxman]

Thank you!

[Tom]

A < B < C is shorthand for A<B AND B<C.

I assume that filldates and days_supply are array names and i is the index into the array.  Although they could be user defined functions.

Stick your condition into a WHERE statement and SAS will show you how it is interpreted in the LOG.

908   data _null_;
909     set sashelp.class;
910     where AGE <= HEIGHT <= WEIGHT ;
911   run;

NOTE: There were 18 observations read from the data set SASHELP.CLASS.
      WHERE (AGE<=HEIGHT) and (HEIGHT<=WEIGHT);

[alaxman]

Thank you!

[tarheel13]

It means start_dt + ii -1 is >= filldates(i) AND start_dt + ii - 1 is <= filldates(i) + days_supply(i)-1.