/* Any controlled variable may behave as a stack. */

declare s float controlled;

/* to push a value on the stack. */
allocate s;
s = 10;

/* To pop a value from the stack. */
put (s);
free s;

/* to peek at the top of stack> */
put (s);

/* To see whether the stack is empty */
if allocation(s) = 0 then ...

/* Note: popping a value from the stack, or peeking,          */
/* would usually require a check that the stack is not empty. */

/* Note: The above is a simple stack for S. */
/* S can be any kind of data structure, an array, etc. */

/* Example to push ten values onto the stack, and then to */
/* remove them.                                           */

/* Push ten values, obtained from the input, onto the stack: */
declare S float controlled;
do i = 1 to 10;
   allocate s;
   get list (s);
end;
/* To pop those values from the stack: */
do while (allocation(s) > 0);
   put skip list (s);
   free s;
end;
/* The values are printed in the reverse order, of course. */