These conversion types modify the value returned by %SYSEVALF so that it can be
used in other macro expressions that require integer or Boolean values.
CAUTION:
Specify a conversion type for the %SYSEVALF function. If you use the
%SYSEVALF function in macro expressions or assign its results to macro variables
that are used in other macro expressions, then errors or unexpected results might
occur if the %SYSEVALF function returns missing or floating-point values. To
prevent errors, specify a conversion type that returns a value compatible with other
macro expressions. For more information about using conversion types, see
“%SYSEVALF Function” on page 281.
How the Macro Processor Evaluates Logical
Expressions
Comparing Numeric Operands in Logical Expressions
A logical, or Boolean, expression returns a value that is evaluated as true or false. In the
macro language, any numeric value other than 0 is true and a value of 0 is false.
When the macro processor evaluates logical expressions that contain operands that
represent numbers, it converts the characters temporarily to numeric values. To illustrate
how the macro processor evaluates logical expressions with numeric operands, consider
the following macro definition:
%macro compnum(first,second);
%if &first>&second %then %put &first is greater than &second;
%else %if &first=&second %then %put &first equals &second;
%else %put &first is less than &second;
%mend compnum;
Invoke the COMPNUM macro with these values:
%compnum(1,2)
%compnum(-1,0)
The following results are displayed in the log:
1 is less than 2
-1 is less than 0
The results show that the operands in the logical expressions were evaluated as numeric
values.
Comparing Floating-Point or Missing Values
You must use the %SYSEVALF function to evaluate logical expressions containing
floating-point or missing values. To illustrate comparisons with floating-point and
missing values, consider the following macro that compares parameters passed to it with
the %SYSEVALF function and places the result in the log:
%macro compflt(first,second);
%if %sysevalf(&first>&second) %then %put &first is greater than
&second;
%else %if %sysevalf(&first=&second) %then %put &first equals
78 Chapter 6 • Macro Expressions
&second;
%else %put &first is less than &second;
%mend compflt;
Invoke the COMPFLT macro with these values:
%compflt (1.2,.9)
%compflt (-.1,.)
%compflt (0,.)
The following values are written in the log:
1.2 is greater than .9
-.1 is greater than .
0 is greater than .
The results show that the %SYSEVALF function evaluated the floating-point and
missing values.
Comparing Character Operands in Logical Expressions
To illustrate how the macro processor evaluates logical expressions, consider the
COMPCHAR macro. Invoking the COMPCHAR macro compares the values passed as
parameters and places the result in the log.
%macro compchar(first,second);
%if &first>&second %then %put &first comes after &second;
%else %put &first comes before &second;
%mend compchar;
Invoke the macro COMPCHAR with these values:
%compchar(a,b)
%compchar(.,1)
%compchar(Z,E)
The following results are printed in the log:
a comes before b
. comes before 1
Z comes after E
When the macro processor evaluates expressions with character operands, it uses the sort
sequence of the host operating system for the comparison. The comparisons in these
examples work with both EBCDIC and ASCII sort sequences.
A special case of a character operand is an operand that looks numeric but contains a
period character. If you use an operand with a period character in an expression, both
operands are compared as character values. This can lead to unexpected results. So that
you can understand and better anticipate results, look at the following examples.
Invoke the COMPNUM macro with these values:
%compnum(10,2.0)
The following values are written to the log:
10 is less than 2.0
Because the %IF-THEN statement in the COMPNUM macro uses integer evaluation, it
does not convert the operands with decimal points to numeric values. The operands are
compared as character strings using the host sort sequence, which is the comparison of
characters with smallest-to-largest values. For example, lowercase letters might have
How the Macro Processor Evaluates Logical Expressions 79
smaller values than uppercase, and uppercase letters might have smaller values than
digits.
CAUTION:
The host sort sequence determines comparison results. If you use a macro
definition on more than one operating system, comparison results might differ
because the sort sequence of one host operating system might differ from the other
system. For more information about host sort sequences, see “SORT Procedure” in
Base SAS Procedures Guide.
80 Chapter 6 • Macro Expressions
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