我们可以将您的问题分为两部分.您的标题暗示循环存在问题，但循环与

We can separate your question into two parts. Your title implies a problem with loops, but your loops are just equivalent to

  replace OK = 1 if strpos(ATC, A)!=0

因此循环的使用似乎无关紧要.剩下的子字符串比较.

so the use of looping appears irrelevant. That leaves the substring comparison.

让我们举个例子:

. set obs 3 
obs was 0, now 3

. gen OK = 0 

. gen A = cond(_n == 1, "42", "something else")  

. gen ATC = "answer is 42"

. replace OK = 1 if strpos(ATC, A) != 0 
(1 real change made)

. list 

     +------------------------------------+
    | OK                A            ATC |
    |------------------------------------|
 1. |  1               42   answer is 42 |
 2. |  0   something else   answer is 42 |
 3. |  0   something else   answer is 42 |
    +------------------------------------+

所以工作正常；如果您认为自己有所不同，则确实需要举一个可重复的示例.

So it works fine; and you really need to give a reproducible example if you think you have something different.

关于指定应在何处更改变量:如上例所示，您的代码正是这样做的.

As for specifying where the variable should be changed: your code does precisely that, as again the example above shows.

此更新使问题明确.当您指定所提供的语法时，Stata仅会在相同观察值中查找匹配的子字符串. Stata中的变量是数据集中的字段.要遍历一组值，应满足以下条件

The update makes the problem clear. Stata will only look in the same observation for a matching substring when you specify the syntax you gave. A variable in Stata is a field in a dataset. To cycle over a set of values, something like this should suffice

 gen byte OK = 0 
 levelsof A, local(Avals) 

 quietly foreach A of local Avals { 
     replace OK = 1 if strpos(ATC, `"`A'"') > 0 
 } 

注意:

1. 指定byte会减少存储量.

您可能需要对levelsof进行if或in限制.

You may need an if or in restriction on levelsof.

quietly剪切有关更改值的消息.调试时，通常***将其排除在外.

quietly cuts out messages about changed values. When debugging, it is often better left out.

> 0，因为在逻辑比较中自动将来自strpos()的肯定结果视为true.请参阅此常见问题解答.

> 0 could be omitted as a positive result from strpos() is automatically treated as true in logical comparisons. See this FAQ.