You are permitted, and encouraged, to work together on these problems,
provided that every contributor understands how the complete solution
was found. Put the names of all contributors into comments at the top of
your C file:

   /* assignment 5 */
   /* Joe Bloggs */
   /* Alice Smith */

Your solutions are due Friday 5 October at 17:00. Send each C file in
a separate email message to djb-275-hw@cr.yp.to:

   mail djb-275-hw@cr.yp.to < ex5.c
   mail djb-275-hw@cr.yp.to < ex6.c

You are permitted to use putchar(), getchar(), scanf(), malloc(), and
free() in these problems.


5. Write a dbl program that prints two copies of its input. For example,
if the user types

   one two
   three

then dbl prints

   one two
   three
   one two
   three

The amount of memory used by your program must be proportional to the
size of the input. If not enough memory is available, print a message
and exit.


6. Write a dblline program that prints two copies of each line of input.
For example, if the user types

   one two
   three

then dblline prints

   one two
   one two
   three
   three

The amount of memory used by your program must be proportional to the
size of the longest line of input. If not enough memory is available,
print a message and exit.