Conditional statements (if-then statements, if-then-else statements) are often used to assign values to variables. Example:
data new; input prefix age sex $; if prefix=821 then city='auburn'; if age <30 then young=1; else young=0; if age<30 and sex='f' then yw=1; if age>80 or prefix='749' then nogood=1; .....
The logical connectives AND and OR are used to create compound tests, as illustrated above.
A counterless do-loop can be used to have more complicated processing after an if-branch. Example:
if age<30 then do; if income<20000 then cat=1; if income>20000 and income <30000 then cat=2; end; ....
The return statement can be used to branch to the bottom of the data step program.
Do-loops and if-then statements can be nested.