WHILE 循环中的 sy-index

Question

I wrote a program to count the number of each vowel in a string character.

Here is the code:

    DATA: v_nom(10)  TYPE c VALUE 'christian',
          vowels     TYPE string,
          lenght     TYPE i,
          char       TYPE c,
          occurences TYPE i,
          index      TYPE i.
    
    vowels ='aeiouy'.
    lenght =  strlen( vowels ).
    
    index = sy-index.
    
    WRITE index.
    
    WHILE index < lenght.
    
      char = vowels+index.
    
      FIND ALL OCCURRENCES OF char IN v_nom MATCH COUNT occurences.
    
    
      ADD 1 TO index.
    
      IF occurences = 0.
    
      ELSE.
    
     write:/ char, 'appears',/ occurences, 'times'.
    
      ENDIF.
    ENDWHILE.

It works fine... but at first I try do it by using directly sy-index without assigning it to a variable, an the problem when I run the debug I saw that sy-index starts at the position 1, not 0.

Using a variable or using directly the system variable should work the same?

Here is the code:

DATA: v_nom(10)  TYPE c VALUE 'christian',
      vowels     TYPE string,
      lenght     TYPE i,
      char       TYPE c,
      occurences TYPE i.

vowels ='aeiouy'.
lenght =  strlen( vowels ).


WHILE sy-index < lenght.

  char = vowels+sy-index.

  FIND ALL OCCURRENCES OF char IN v_nom MATCH COUNT occurences.
  ADD 1 TO index.

  IF occurences = 0.

  ELSE.

 write:/ char, 'appears',/ occurences, 'times'.

  ENDIF.
ENDWHILE.

Sy-index starts at pos 1 not 0, by the letter 'e' not with the first one which is 'a'....

Can someone tell me where I make a mistake....

Regards.

Answer 1

Name	Type	Length	Content
sy-index	i	-	Loop index. In DO and WHILE loops, contains the number of previous loop passes, including the current pass.

Within the statement block, the system field sy-index contains the number of previous loop passes, including the current pass.

Documentation .

Now in your example you assign sy-index before you reach the loop. Hence it will have it's initial value, which is 0 for type i .
If you use it within the loop, the first iteration will have 1 (number of previous loop passes, including the current pass).
And yes, ABAP is a 1-based language. The first line of an internal table is also lt_sflight[ 1 ] , not lt_sflight[ 0 ] .

Answer 2

Note that this can be solved way easier with count_any_of :

DATA(occurences) = count_any_of( 
  val = v_nom
  sub = 'aeiouy'
).