Example of Recursive Routines

The following sample code illustrates some of the features of a recursive routine. This routine, identified by the entry point factorl, computes the factorial of a number that you enter.

 1 working-storage section.
 2 01 n             pic x(4) comp-x.
 3 01 factorial     pic x(4) comp-x.
 4 01 m             pic x(4) comp-x.
 5
 6 local-storage section.
 7
 8 procedure division.
 9     accept n
10     move 1 to factorial
11     call 'factorl' using n
12     display 'factorial of ' n ' is ' factorial
13     stop run.
14
15 entry 'factorl' using m.
16     if m < 1
17         move 1 to factorial
18     else
19         if m > 1
20             multiply m by factorial
21             subtract 1 from m
22             call 'factorl' using m
23         end-if
24     end-if
25
26     exit program.

Note:

Line 6
local-storage section

Since the recursive routine can be called several times, the local data from one call must be protected from another call to the same code. This protection is done using a Local-Storage Section. Each time a new instance of the routine starts, an initialized copy of this section is created in memory. If you try to use recursion in a program that does not contain a Local-Storage Section, an RTS error message is issued.

Notice that this routine does not have any local storage data items, but it still requires the local storage declaration.
Line 15
entry 'factorl' using m

This is the entry point of the recursive routine factorl. A program can call itself via its Program-ID or an entry point.
Lines 19-23
if m > 1

multiply m by factorial

subtract 1 from m

call 'factorl' using m

end-if

This loop contains the recursive call.
Line 22
call 'factorl' using m

The recursive call statement.