Structure of SAS                                   Fall 1992
    SAS Primer
Structure of a SAS Program

This section of the manual describes the structure of a SAS program
and the syntax of the language.  Many of the most common mistakes made
when programming SAS are listed in Appendix 1.

SAS Program Blocks:  The DATA step and the PROC step

All SAS programs consist of at least two blocks of statements: the
DATA step and the PROC step.  A step is just a group of program
statements that provide instructions to SAS for entering and modifying
data (the DATA step) or analyzing data (the PROC step).

Use the DATA step to read in and modify data.  A data step begins with
the statement:

DATA setname ;

 and ends with one of the following statements:

RUN;
PROC procedure_name ;

or when another DATA step starts. Between the beginning and ending
statements will be statements for reading data, labeling data, and
performing calculations.  The collection of data values you read in or
create is called a data set and has the name, setname , that you
choose.  If you need to modify your data (such as transform the data
or create new data elements) you must do so in a DATA step, not in a
PROC step.

Use the PROC step to analyze and view your data.  In a PROC step you
can select the type of analysis (regression, analysis of variance,
computation of means) for your data set.  PROC steps begin with the
statement:

PROC  procedure_name ;

 and end with either one of the following statement:

DATA setname ;

or when another PROC step starts.  Other statements used in the PROC
step specify the results you want computed and displayed by the SAS
procedure named procedure_name .

DATA and PROC steps can appear in any order (except, of course, that a
PROC cannot operate on a data set that has not yet been created) and
any number of DATA steps or PROC steps can be used in a program.  It
is important to understand the concept of steps because although some
SAS statements can be used anywhere, many SAS statements are used
exclusively in a DATA step and others are used exclusively in a PROC
step.  It is not uncommon to have to begin a new DATA step in order to
perform necessary data manipulations.

Syntax for SAS Statements

A SAS statement is a string of keywords, names, and symbols ending in
a semicolon.  You may use upper or lower case when typing SAS
statements.  Most SAS statements are specified with the following
form:

keyword parameter  [options]

Such a SAS statements begin with a keyword identifying the kind of a
statement it is.  Some of the identifying keywords are DATA, PROC,
OUTPUT, INFILE, FILE, and VAR.  Parameters are often the names of your
variables or data sets.  Options are keywords specific to a particular
SAS statement.  Assignment statements used to create new variables or
modify the values of existing variables have the familiar algebraic
form you use when calculating these variables by hand.  SAS statements
end with a semicolon (;).
     
     COMMON ERROR:  A missing semicolon is a very
     common syntax error and one that is hard for SAS
     error checking procedures to identify.  For this
     reason the error messages you receive are often
     unclear.

SAS statements are free-format.  This means a statement can begin and
end anywhere on a line, one statement can continue over several lines,
several statements can be on one line, and as many blanks as you like
can be used to separate fields.
     
     PROGRAMMING TIP:  You can make your SAS code
     easier to read and debug by beginning PROC
     statements and DATA statements in the first space
     of the line and indenting all other statements.
     Adding a blank line and comment between steps is
     also helpful.

Rules for SAS Names

SAS uses names to identify variable names, data sets, formats, arrays,
libraries and files.  SAS names must conform to the following rules:

     (1)  no longer than eight characters
     (2)  the first character must be a letter
     (3)  Contain only letters, numbers, or underscores
  
  Comment Statements

Use comment statements to make your program easier to read and edit.
SAS ignores comment statements.  The comment statements will be
printed to your log file.  There are two ways to make a comment
statement:



(1) Put an asterisk, *, at the beginning of a line, write
the comment, and terminate the comment with a semicolon.
For example,

00001 *This is a one-line comment; A Statement following
here is not ignored;



(2)  Start a block of comment lines with /*.  Write as many
comment lines as you want.  Terminate the comment with */.
For example,


00007 /* This is a multi-line comment.  You may want to use
00008	this technique to "turn off" sections of your program.
00009   SAS will ignore all three of these lines*/

     
     PROGRAMMING TIP:  You can use comment statements;
     to "turn off" sections of your code;  this way you
     can avoid looking through unwanted output.