Difference between CHANGING and USING

Question

explain the concept of formal and acutal parameters... when we use changing
and when we use value with simple easy examples...
thanks
Message was edited by:
        balaji velpuri

Answer 1

PROGRAM form_test.
DATA: a1    TYPE p DECIMALS 3,
      a2    TYPE i,
      a3    TYPE d,
      a4    TYPE spfli-carrid,
      a5(1) TYPE c.
PERFORM subr USING a1 a2 a3 a4 a5.
PERFORM subr CHANGING a1 a2 a3 a4 a5.
PERFORM subr USING a1 a2 a3
             CHANGING a4 a5.
FORM subr USING
            value(f1) TYPE p
            value(f2) TYPE i
            f3        LIKE a3
          CHANGING
            value(f4) TYPE spfli-carrid
            f5.
ENDFORM.
This example defines a subroutine subr with a parameter interface consisting of five formal parameters, f1 to f5. The subroutine is called internally three times. The actual parameters are the data objects a1 to a5. The three subroutine calls are all equally valid. There are further PERFORM statements that are also equally valid, so long as the sequence of the actual parameters remains unchanged. In each call, a1 is passed to f1, a2 to f2, and so on. When the subroutine ends, a3, a4, and a5 receive the values of f3, f4, and f5 respectively. The third of the subroutine calls documents in the program what the parameter interface of the subroutine shows, namely that only a4 and a5 are changed. In the case of reference parameter f3, it depends on the programming of the subroutine whether a3 is changed all the same.
REPORT demo_mod_tech_describe.
DATA:
  date1      TYPE d,             date2      TYPE t,
  string1(6) TYPE c,             string2(8) TYPE c,
  number1    TYPE p DECIMALS 2,  number2    TYPE p DECIMALS 0,
  count1     TYPE i,             count2     TYPE i.
PERFORM typetest USING date1 string1 number1 count1.
SKIP.
PERFORM typetest USING date2 string2 number2 count2.
FORM typetest USING now
                    txt TYPE c
                    value(num) TYPE p
                    int TYPE i.
  DATA: t(1) TYPE c.
  DESCRIBE FIELD now TYPE t.
  WRITE: / 'Type of NOW is', t.
  DESCRIBE FIELD txt LENGTH t IN CHARACTER MODE.
  WRITE: / 'Length of TXT is', t.
  DESCRIBE FIELD num DECIMALS t.
  WRITE: / 'Decimals of NUM are', t.
  DESCRIBE FIELD int TYPE t.
  WRITE: / 'Type of INT is', t.
ENDFORM.
This produces the following output:
Type of NOW is D
Length of TXT is 6
Decimals of NUM are 2
Type of INT is I
Type of NOW is T
Length of TXT is 8
Decimals of NUM are 0
Type of INT is I
Regards,
Pavan