SAS Constants in Expressions
Definition
A SAS constant is a number or a character string that indicates a fixed value. Constants
can be used as expressions in many SAS statements, including variable assignment and
IF-THEN statements. They can also be used as values for certain options. Constants are
also called literals.
The following are types of SAS constants:
• character
• numeric
• date, time, and datetime
• bit testing
Character Constants
A character constant consists of 1 to 32,767 characters and must be enclosed in quotation
marks. Character constants can also be represented in hexadecimal form.
Using Quotation Marks with Character Constants
In the following SAS statement, Tom is a character constant:
if name='Tom' then do;
If a character constant includes a single quotation mark, enclose it in double quotation
marks. For example, to specify the character value Tom's as a constant, enter the
following:
name="Tom's"
Another way to write the same string is to enclose the string in single quotation marks
and to express the apostrophe as two consecutive quotation marks. SAS treats the two
consecutive quotation marks as one quotation mark:
name='Tom''s'
The same principle holds true for double quotation marks:
name="Tom""s"
CAUTION:
Matching quotation marks correctly is important. Missing or extraneous quotation
marks cause SAS to misread both the erroneous statement and the statements that
follow it. For example, in name='O'Brien';, O is the character value of Name,
Brien is extraneous, and '; begins another quoted string.
SAS Constants in Expressions 93
Comparing Character Constants and Character Variables
It is important to remember that character constants are enclosed in quotation marks, but
names of character variables are not. This distinction applies wherever you can use a
character constant, such as in titles, footnotes, labels, and other descriptive strings; in
option values; and in operating environment-specific strings, such as file specifications
and commands.
The following statements use character constants:
• x='abc';
• if name='Smith' then do;
The following statements use character variables:
• x=abc;
• if name=Smith then do;
In the second set of examples, SAS searches for variables named ABC and SMITH,
instead of constants.
Note: SAS distinguishes between uppercase and lowercase when comparing character
expressions. For example, the character values 'Smith' and 'SMITH' are not
equivalent.
Character Constants Expressed in Hexadecimal Notation
SAS character constants can be expressed in hexadecimal notation. A character
hexadecimal constant is a string of an even number of hexadecimal characters enclosed
in single or double quotation marks, followed immediately by an X, as in this example:
'534153'x
A comma can be used to make the string more readable, but it is not part of and does not
alter the hexadecimal value. If the string contains a comma, the comma must separate an
even number of hexadecimal characters within the string, as in this example:
if value='3132,3334'x then do;
Note: Any trailing blanks or leading blanks within the quotation marks cause an error
message to be written to the log.
Numeric Constants
A numeric constant is a number that appears in a SAS statement. Numeric constants can
be presented in many forms, including
• standard notation
• scientific (E) notation
• hexadecimal notation
Numeric Constants Expressed in Standard Notation
Most numeric constants are written just as numeric data values are. The numeric
constant in the following expression is 100:
94 Chapter 6 • Expressions
part/all*100
Numeric constants can be expressed in standard notation in the following ways:
Table 6.1 Standard Notation for Numeric Constants
Numeric Constant Description
1 is an unsigned integer
–5 contains a minus sign
+49 contains a plus sign
1.23 contains decimal places
01 contains a leading zero, which is not
significant
Numeric Constants Expressed in Scientific Notation
In scientific notation, the number before the E is multiplied by the power of ten that is
indicated by the number after the E. For example, 2E4 is the same as 2x10
4
or 20,000.
For numeric constants larger than (10
32
)−1, you must use scientific notation. Additional
examples follow:
• 1.2e23
• 0.5e-10
Numeric Constants Expressed in Hexadecimal Notation
A numeric constant that is expressed as a hexadecimal value starts with a numeric digit
(usually 0), can be followed by more hexadecimal characters, and ends with the letter X.
The constant can contain up to 16 valid hexadecimal characters (0 to 9, A to F). The
following are numeric hexadecimal constants:
• 0c1x
• 9x
You can use numeric hexadecimal constants in a DATA step, as follows:
data test;
input abend pib2.;
if abend=0c1x or abend=0b0ax then do;
more SAS statements
run;
Date, Time, and Datetime Constants
You can create a date constant, time constant, or datetime constant by specifying the date
or time in single or double quotation marks, followed by a D (date), T (time), or DT
(datetime) to indicate the type of value.
SAS Constants in Expressions 95
Any trailing blanks or leading blanks included within the quotation marks do not affect
the processing of the date constant, time constant, or datetime constant.
Use the following patterns to create date and time constants:
'ddmmm<yy>yy'D or “ddmmm<yy>yy”D represents a SAS date value:
• date='1jan2013'd;
• date='01jan09'd;
'hh:mm<:ss.s>'T or “hh:mm<:ss.s>”T represents a SAS time value:
• time='9:25't;
• time='9:25:19pm't;
'ddmmm<yy>yy:hh:mm<:ss.s>'DT or “ddmmm<yy>yy:hh:mm<:ss.s>”DT represents a
SAS datetime value:
• if begin='01may12:9:30:00'dt then
end='31dec13:5:00:00'dt;
• dtime='18jan2003:9:27:05am'dt;
'yyyy-mm-ddThh:mm:ssZ'DT or 'yyyy-mm-ddThh:mm:ss+|-hh:ss'DT represent a SAS
datetime constant for Universal Coordinate Time (UTC) based on the ISO 8601
standard.
• tstamp='2013-05-17T09:15:30–05:00'dt; and
tstamp='2013-05-17T09:15:30–05'dt; specifies the UTC for Eastern
Standard Time.
• tstamp='2013-07-20T12:00:00+00:00'dt; and
tstamp='2013-07-20T12:00:00Z'dt; specifies the UTC for the zero
meridian near Greenwich, England.
For more information about SAS dates, see Chapter 7, “Dates, Times, and Intervals,” on
page 111.
Bit Testing Constants
Bit masks are used in bit testing to compare internal bits in a value's representation. You
can perform bit testing on both character and numeric variables. The general form of the
operation is:
expression comparison-operator bit-mask
The following are the components of the bit-testing operation:
expression
can be any valid SAS expression. Both character and numeric variables can be bit
tested. When SAS tests a character value, it aligns the left-most bit of the mask with
the left-most bit of the string; the test proceeds through the corresponding bits,
moving to the right. When SAS tests a numeric value, the value is truncated from a
floating-point number to a 32-bit integer. The right-most bit of the mask is aligned
with the right-most bit of the number, and the test proceeds through the
corresponding bits, moving to the left.
comparison-operator
compares an expression with the bit mask. See “Comparison Operators” on page
101for a discussion of these operators.
bit-mask
is a string of 0s, 1s, and periods in quotation marks that is immediately followed by a
B. Zeros test whether the bit is off; ones test whether the bit is on; and periods ignore
96 Chapter 6 • Expressions
the bit. Commas and blanks can be inserted in the bit mask for readability without
affecting its meaning.
CAUTION:
Truncation can occur when SAS uses a bit mask. If the expression is longer than
the bit mask, SAS truncates the expression before it compares it with the bit mask. A
false comparison might result. An expression's length (in bits) must be less than or
equal to the length of the bit mask. If the bit mask is longer than a character
expression, SAS prints a warning in the log, stating that the bit mask is truncated on
the left, and continues processing.
The following example tests a character variable:
if a='..1.0000'b then do;
If the third bit of A (counting from the left) is on, and the fifth through eighth bits are
off, the comparison is true and the expression result is 1. Otherwise, the comparison is
false and the expression result is 0. The following is a more detailed example:
data test;
input @88 bits $char1.;
if bits='10000000'b
then category='a';
else if bits='01000000'b
then category='b';
else if bits='00100000'b
then category='c';
run;
Note: Bit masks cannot be used as bit literals in assignment statements. For example,
the following statement is not valid:
x='0101'b; /* incorrect*/
The $BINARYw. and BINARYw. formats and the $BINARYw., BINARYw.d, and
BITSw.d informats can be useful for bit testing. You can use them to convert character
and numeric values to their binary values, and vice versa, and to extract specified bits
from input data. See SAS Formats and Informats: Reference for complete descriptions of
these formats and informats.
Avoiding a Common Error with Constants
When you use a string in quotation marks followed by a variable name, always put a
blank space between the closing quotation mark and the variable name. Otherwise, SAS
might interpret a character constant followed by a variable name as a special SAS
constant as illustrated in this table.
Table 6.2 Characters That Cause Misinterpretation When Following a Character Constant
Characters That Follow a
Character Constant Possible Interpretations Examples
b bit testing constant '00100000'b
d date constant '01jan04'd
dt datetime constant '18jan2005:9:27:05am'dt
SAS Constants in Expressions 97
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