COBOL Beer on the Wall Program

Question

我做的"99瓶“计划，但与用户输入了多少下来。我对COBOL非常陌生，我肯定忽略了一些简单的东西，或者只是完全用错误的方式思考这个问题。

以下是我目前的情况：

   IDENTIFICATION DIVISION.
   PROGRAM-ID. HW.

   DATA DIVISION.
   WORKING-STORAGE SECTION.
   01 COUNTER                      PIC S99.
   01 BOTTLES                      PIC Z9.
   01 BOTTLES-REMAINING            PIC Z9.
   01 NUM                          PIC s9(02) VALUE 0.

   PROCEDURE DIVISION.
       PERFORM VARYING COUNTER FROM 99 BY NUM UNTIL COUNTER = 0
         DISPLAY "How many bottles would you like to take down?"
         ACCEPT NUM
         MOVE COUNTER to Bottles
         subtract NUM FROM COUNTER GIVING BOTTLES-REMAINING
         DISPLAY SPACES
         EVALUATE COUNTER
           WHEN 1
             DISPLAY " 1 bottle of beer on the wall, "
                     "  1 bottle of beer."
             DISPLAY "Take one down and pass it around, "
                     "no more bottles of beer on the wall."
           WHEN 2 Thru 99
             DISPLAY BOTTLES " bottles of beer on the wall, "
                     BOTTLES " bottles of beer."
             DISPLAY "Take one down and pass it around, "
                     BOTTLES-REMAINING
                     " bottles of beer on the wall."
         END-EVALUATE
       END-PERFORM
     GOBACK.

我需要使NUM子句在以下语句(或数据除法)中为负值，这样它将从计数器中减去：

       PERFORM VARYING COUNTER FROM 99 BY NUM UNTIL COUNTER = 0

Answer 1

我在这里看到了一些问题。

首先，这是从已褪色的内存中得到的，但我似乎还记得，VARYING子句对于增量需要一个常量值。我认为您无法使用实际更改的NUM来完成此操作。

因此，您的循环最好不要使用VARYING子句，而是类似于(这里的代码在语法上可能不是正确的COBOL，它更多地是为了显示意图和/或方法)：

set counter to 99
perform until counter = 0
    blah blah blah then change counter
end perform

第二，如果允许你一次拿出一个以上的瓶子，你的小曲就不再有意义了。押韵第三节的语句应修改为类似于瓶左节：

evaluate num
    when 1
        display "Take one down and pass it around, "
    when 2 thru 99
        display "Take ", num, " down and pass them around, "
end evaluate

最后，您可能希望避免这样的情况:您移除的瓶子比现有的(或少于一个)更多。这可以通过在获得用户输入后立即执行这些限制(夹紧)来实现：

accept num
if num is less than one
    set num to one
end if
if num is greater than counter
    set num to counter
end if

您也可以抱怨并要求用户输入有效的数量，但最简单的解决方案可能只是将其夹住。