How to replace spaces at the right into zeros at the left in COBOL?

Question

I have an alphanumeric variable with a length of 10. It contains a number at the beginning, the rest of the digits are filled with spaces. Then I need to move the string to the

Answer 1

Bill Woodger mentioned: "There are also ... byte-by-byte MOVEs (sometimes preferred by "traditionalists", but the least clear of the lot)." Here is one such solution that I hope is reasonably clear. Below are two version. First, a solution updated for the suggestions below. Second, the original solution proposed, to reference in understanding the comments made. Thank you, Bill, for your good suggestions! I might learn to write good COBOL one of these days :)

   IDENTIFICATION DIVISION.
   PROGRAM-ID. SHIFT-RIGHT.
  * SITUATION ON STACKOVERFLOW.COM:
  * I HAVE AN ALPHANUMERIC VARIABLE WITH A LENGTH OF 10. 
  * IT CONTAINS A NUMBER AT THE BEGINNING, THE REST OF THE DIGITS 
  * ARE FILLED WITH SPACES. THEN I NEED TO MOVE THE STRING TO THE 
  * LEFT AND PUT THE NUMBER OF SPACES WITH '0' AT THE BEGINING. 
  * THIS EXAMPLES SPEAKS FOR THEMSELVES:

  * INPUT            OUTPUT
  * ==============================
  * '123456    ' ->  '0000123456'
  * '12345678  ' ->  '0012345678'
  * '123456789 ' ->  '0123456789'
  * '1234567890' ->  '1234567890'
  *
  * ASSUME INPUT DATA VALIDATION DONE ELSEWHERE.


   ENVIRONMENT DIVISION.
   INPUT-OUTPUT SECTION.
   FILE-CONTROL.

   DATA DIVISION.
   FILE SECTION.

   WORKING-STORAGE SECTION.
   01  STRING-IN                   PIC X(10).
   01  STRING-OUT                  PIC X(10).
   01  STRING-LENGTH               PIC 99 USAGE COMP.
   01  CHAR-IN-NUM                 PIC 99 USAGE COMP.
   01  CHAR-OUT-NUM                PIC 99 USAGE COMP.

   PROCEDURE DIVISION.
   MAIN.
       PERFORM INITIALIZE-LENGTH
       MOVE '123456    ' TO STRING-IN
       PERFORM MAKE-AND-SHOW
       MOVE '12345678  ' TO STRING-IN
       PERFORM MAKE-AND-SHOW
       MOVE '123456789 ' TO STRING-IN
       PERFORM MAKE-AND-SHOW
       MOVE '1234567890' TO STRING-IN
       PERFORM MAKE-AND-SHOW
       MOVE SPACES TO STRING-IN
       PERFORM MAKE-AND-SHOW
       STOP RUN
       .

   INITIALIZE-LENGTH.
       MOVE LENGTH OF STRING-IN TO STRING-LENGTH
       IF LENGTH OF STRING-OUT NOT = STRING-LENGTH
           DISPLAY 'LENGTH OF STRING-IN, ' STRING-LENGTH ', '
                   'NOT EQUAL TO LENGTH OF STRING-OUT, '
                   LENGTH OF STRING-OUT
           STOP RUN
       END-IF
       .

   MAKE-AND-SHOW.
       PERFORM MAKE-STRING-OUT
       PERFORM SHOW-BEFORE-AFTER
       .

   MAKE-STRING-OUT.
       MOVE ZEROS         TO STRING-OUT
       MOVE STRING-LENGTH TO CHAR-OUT-NUM
                             CHAR-IN-NUM
       PERFORM STRING-LENGTH TIMES
           IF STRING-IN (CHAR-IN-NUM:1) NOT = SPACE
               MOVE STRING-IN (CHAR-IN-NUM:1) 
                 TO STRING-OUT (CHAR-OUT-NUM:1)
               SUBTRACT 1 FROM CHAR-OUT-NUM
           END-IF
           SUBTRACT 1 FROM CHAR-IN-NUM
       END-PERFORM
       .

   SHOW-BEFORE-AFTER.
       DISPLAY "STRING IN:  '" STRING-IN "'"
       DISPLAY "STRING OUT: '" STRING-OUT "'"
       DISPLAY " "
       .


  **********************************************
  * EARLIER VERSION, BEFORE IMPROVEMENTS 
  * SUGGESTED IN COMMENTS
  **********************************************

   IDENTIFICATION DIVISION.
   PROGRAM-ID. SHIFT-LEFT.
  * SITUATION ON STACKOVERFLOW.COM:
  * I HAVE AN ALPHANUMERIC VARIABLE WITH A LENGTH OF 10. 
  * IT CONTAINS A NUMBER AT THE BEGINNING, THE REST OF THE DIGITS 
  * ARE FILLED WITH SPACES. THEN I NEED TO MOVE THE STRING TO THE 
  * LEFT AND PUT THE NUMBER OF SPACES WITH '0' AT THE BEGINING. 
  * THIS EXAMPLES SPEAKS FOR THEMSELVES:

  * INPUT            OUTPUT
  * ==============================
  * '123456    ' ->  '0000123456'
  * '12345678  ' ->  '0012345678'
  * '123456789 ' ->  '0123456789'
  * '1234567890' ->  '1234567890'
  *
  * ASSUME INPUT DATA VALIDATION DONE ELSEWHERE.


   ENVIRONMENT DIVISION.
   INPUT-OUTPUT SECTION.
   FILE-CONTROL.

   DATA DIVISION.
   FILE SECTION.

   WORKING-STORAGE SECTION.
   01  STRING-IN                   PIC X(10).
   01  STRING-OUT                  PIC X(10).
   01  CHAR-IN-NUM                 PIC 99 USAGE COMP-3.
   01  CHAR-OUT-NUM                PIC 99 USAGE COMP-3.

   PROCEDURE DIVISION.
   MAIN.
       MOVE '123456    ' TO STRING-IN
       PERFORM MAKE-AND-SHOW
       MOVE '12345678  ' TO STRING-IN
       PERFORM MAKE-AND-SHOW
       MOVE '12345678  ' TO STRING-IN
       PERFORM MAKE-AND-SHOW
       MOVE '123456789 ' TO STRING-IN
       PERFORM MAKE-AND-SHOW
       MOVE '1234567890' TO STRING-IN
       PERFORM MAKE-AND-SHOW

       STOP RUN
       .

   MAKE-AND-SHOW.
       PERFORM MAKE-STRING-OUT
       PERFORM SHOW-BEFORE-AFTER
       .

   MAKE-STRING-OUT.
       MOVE SPACES TO STRING-OUT
       MOVE 10     TO CHAR-OUT-NUM
       PERFORM VARYING CHAR-IN-NUM FROM 10 BY -1
           UNTIL CHAR-IN-NUM < 1
           IF STRING-IN (CHAR-IN-NUM:1) NOT = SPACE
               MOVE STRING-IN (CHAR-IN-NUM:1) 
                 TO STRING-OUT (CHAR-OUT-NUM:1)
               SUBTRACT 1 FROM CHAR-OUT-NUM
           END-IF
       END-PERFORM
       PERFORM UNTIL CHAR-OUT-NUM < 1
           MOVE ZERO TO STRING-OUT (CHAR-OUT-NUM:1)
           SUBTRACT 1 FROM CHAR-OUT-NUM
       END-PERFORM
       .

   SHOW-BEFORE-AFTER.
       DISPLAY "STRING IN:  '" STRING-IN "'"
       DISPLAY "STRING OUT: '" STRING-OUT "'"
       DISPLAY " "
       .