写了一段宏，怎么都测试不出结果。数据格式如下，计算过程是：1。先判断count12是否有数，有的话，取其具體数的绝对值，即是其对应的月份的IOP进行相减。如：count21=15，其前面count11=9，则IOP_15m-IOP_9m.中間鑲嵌了一段判斷具體是哪一類相減，一共6種，包括（IOP_B_B IOP_PGA IOP_Miotic IOP_CAI IOP_Diamox IOP_Adren）.

每次程序都報錯說：ERROR: A character operand was found in the %EVAL function or %IF condition where a numeric operand is required. The condition was: count21
我檢查過了，count21都是數值型，所以不是這個的問題，懷疑是數據讀取的問題，但是自己怎麼也發現不了。還望有高手來救我。

count11	count21	count31	IOP_3m	IOP_6m	IOP_9m	IOP_12m	IOP_15m	IOP_18m
9	15	18	15	16	21	18	19	20
			17	17	18	19	15	16
-12	15	18	16	21	18	15	16	21
3	6		17	18	19	17	17	18

%macro IOP12(i=);
  %let x=%eval(count&i.1);
  %let j=%eval(&i-1);
  %let b=%eval(count&j.1);
data IOP1_begin3m;
set IOP1_begin3m;
if abs(coun&i.1)>0 then do;
   if B_B_&x.M_c ~= B_B_&b.M_c then IOP_B_B=IOP_&x.M-IOP_&b.M;
     else if  PGA_&x.M_c ~= PGA_&b.M_c then IOP_PGA=IOP_&x.M-IOP_&b.M;
     else if  Miotic_&x.M_c ~= Miotic_&b.M_c then IOP_Miotic=IOP_&x.M-IOP_&b.M;
     else if  CAI_&x.M_c ~= CAI_&b.M_c then IOP_CAI=IOP_&x.M-IOP_&b.M;
     else if  Diamox_&x.M_c ~= Diamox_&b.M_c then IOP_Diamox=IOP_&x.M-IOP_&b.M;
     else if  Adren_&x.M_c ~= Adren_&b.M_c then IOP_Adren=IOP_&x.M-IOP_&b.M;
end;
run;
%mend IOP12;

%IOP12(i=2);