1%let a=cat;
%macro animal(a=frog) ;
%let a=bird;
%mend;
%animal(a=pig);
%put a is &a;


2%let a=cat;
%macro animal;
%let a=dog;
%mend;
%animal;
%put a is &a;

第一个程序log里面是a is cat ，第二个是a is dog，global和local macro variable 我有些分不清楚，望大家解答~谢谢