1. How SAS implements structured programming constructs
Programming in SAS
How SAS implements structured programming constructs

2. SAS Philosophy The “Elephant philosophy of programming”
Remove everything that doesn’t look like an elephant.
SAS manipulates tables one row at a time.

3. DATA Steps Program statements are executed within data steps
Code is executed in the order that it appears
Instruction sets in SAS end with a DATA, PROC, or RUN statement
Each DATA step executes an implied loop from the first read statement (SET, MERGE, INPUT, etc.) to the start of the next instruction set
Data records are output at the end of the instruction set (implied OUTPUT) unless there is an OUTPUT statement

4. Sequence
Statement 1
Statement 2
Statement 3
Statement 4
Statement …

5. Loops Setup Statements Setup Statements DO WHILE Statement 1
Statement n
***
DO UNTIL
Statement 1
Statement 2
Statement 3
Statement n
***

6. DO Statement DO; ...more SAS statements... END;
DO index-variable=specification-1 <, specification-n>; more SAS statements . . .

7. DO WHILE|UNTIL Statement
The UNTIL expression is evaluated at the bottom of the loop after the statements in the DO loop have been executed. If the expression is true, the DO loop does not iterate again.
The WHILE expression is evaluated at the top of the loop before the statements in the DO loop are executed. If the expression is true, the DO loop iterates. If the expression is false the first time it is evaluated, the DO loop does not iterate even once.

8. Examples
n=0;
do while(n<5);
n= n+1;
put n;
end;
do until (n<5);

9. Examples do i=1 to 10; do count=2 to 8 by 2;
do i=1 to 10 while (x<y);
do i=2 to 20 by 2 until((x/3)>y);

10. Selection Select Case 1 Case 2 Case 3 Statement 1a Statement 1b
Statement 1c
Statement 2a
Statement 2b
Statement 2c
Statement 3a
Statement 3c
Statement 3c
Statement …
Statement …
Statement …

11. IF-THEN/ELSE Statement
IF expression THEN statement; <ELSE statement;>
Arguments
expression
is any SAS expression and is a required argument.
statement
can be any executable SAS statement or DO group.

12. SAS Selection Constructs
IF … THEN …; ELSE …;
IF … THEN
DO;
Statements
END
ELSE
END;
Other else statements.

13. SELECT Statement
SELECT <(select-expression)>;
WHEN-1 (when-expression-1 <..., when-expression-n>) statement;
<... WHEN-n (when-expression-1 <..., when-expression-n>) statement;>
<OTHERWISE statement;
END;
(select-expression) specifies any SAS expression that evaluates to a single value.
(when-expression) specifies any SAS expression, including a compound expression.

14. SAS Selection Constructs (cont.)
SELECT (payclass);
WHEN ('monthly') amt=salary;
WHEN ('hourly')
DO;
amt=hrlywage*min(hrs,40);
IF hrs>40 THEN PUT 'Check Timecard';
END; /* end of do */
OTHERWISE PUT 'Problem Observation';
END;