大家来看看这个宏 有意思的结果

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今天逛博，无意中看到下面一道趣题，关于宏的：
%macro aa;
%let condition=( 1.2>=1 and 1.2<1.5 ) and ( 1123>=800 and 1123<1200 );

   %if &condition %then %do;
    %put x;
   %end;
   %else %do;
%put M;
   %end;

%let condition=(( 1.2>=1 and 1.2<1.5 ) and ( 1123.1>=800 and 1123.1<1200 ));
   %if &condition %then %do;
    %put Y;
   %end;
   %else %do;
%put N;
   %end;

   %mend aa;
%aa;
跑了下 结果是X N  
很有意思，大家能帮忙解释下吗？

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关键词：有意思 condition dition Macro con

1# sopching


For 2nd condition (1123.1>=800) is FALSE because 1<8 in the character order, and thus the 2nd condition does not meet.
Using %sysevalf(&condition) may get really 'true' result as you expected.
JingJu

2# jingju11
那为什么第一个条件的 不用%sysevalf？1.2<1.5是如何成立的？

sopching 发表于 2010-11-4 00:45
2# jingju11
那为什么第一个条件的 不用%sysevalf？1.2

1=1, .=., 2<5 so 1 . 2 < 1 . 5

赞啊，大师果然厉害！

这个问题的关键在于%IF和%EVAL的运行机制，

%if语句会自动将%eval函数用在%if后的条件上，

%eval的运行：
If all operands can be interpreted as integers, the expression is treated as arithmetic. If at least one operand cannot be interpreted as numeric, the expression is treated as logical. If a division operation results in a fraction, the fraction is truncated to an integer.

所以，如果作为%if的条件,（1123>=800） 的结果就是TRUE（数学运算），而（1123.1>=800）的结果就是FALSE（字符比较）。

例如：
%macro test;
   %if 12>5 %then %put This is OK!;
   %else %put This is not OK!;
   %if 12.0>5.0 %then %put This is right!;
   %else %put This is wrong!;
%mend;

%test

我的猜测也是%if 之后默认加了%eval()运算，而不是%sysevalf()运算，因为那个比较结果和%eval()的方式一致
但是有没有官方的对于
“%if语句会自动将%eval函数用在%if后的条件上”
粗粗查了下，没有找到

帮助里面我也没找到，我是从《SAS macro programming made easy》的165页看到的：
The macro functions that automatically invoke %EVAL around the expressions supplied to them are
      => %SUBSTR and %QSUBSTR
      => %SCAN and %QSCAN
The macro language statements that automatically invoke %EVAL around the expressions supplied to them are
      => %DO
      => %DO %UNTIL
      => %DO %WHILE
      => %IF

经hopewell大大的指点
我在SAS HELP中找到了星星点点的原文

Macro Expressions

How the Macro Processor Evaluates Logical Expressions

......
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.
......
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.


原文以
%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;
调用
%compnum(10,2.0)
出结果
10 is less than 2.0
解释这个现象，应该和楼主的意思是一致的
附上hopewell大大的指点，sas support上的：
All parts of the macro language that evaluate expressions (for example, %IF and %DO statements) call %EVAL to evaluate the condition. For a complete discussion of how macro expressions are evaluated, see Macro Expressions.

http://support.sas.com/documentation/cdl/en/mcrolref/61885/HTML/default/viewer.htm#a000208971.htm

谢谢各位的帮助！我明白他的机制了！