Homework #5

The UNIX Environment

1. (10 points) How would you print the date and time in the form
   

   Friday, May 13 1994 at 01:05AM PDT
   

   Give the UNIX command to do this.

The C Programming Language

2. (50 points) Write a program called choose that prints all permutations of m numbers chosen from the set 1 ... n. Your program is to take two arguments, the first of which is m and the second, n. For example,

   	choose 2 3
   

   would print

   	1 2
   	1 3
   	2 1
   	2 3
   	3 1
   	3 2
   

   (it may print these lines in any order). Put this into a file called choose.c. Remember to look for invalid command line numbers! (Both numbers must be positive, and m <= n.)

   Hint: use recursion.

3. (50 points) The function dyngets is like the function fgets(3) except that it reads lines of arbitrary length, and returns a pointer to dynamically allocated memory containing the current input line. It is useful when the input line can be very, very long.

   A copy of this function is available. Unfortunately, it does not work right. Find, and fix, the error(s). Submit the corrected routine in a file called dyngets.c.

   To get this function, go to the directory ~cs40/hw5 in the CSIF. In that directory are the files dynget.c (the buggy source code) and dyngets.man (a manual page; it describes the arguments and the use of the function). The manual page's description of the function is what the debugged routine should conform to. Also present is a program testdg.c that can be used to test your dyngets function; it too has a manual page and source code in that directory/