CSCI 1120 (Low-Level Computing), Spring 2017:
Homework 5

20 points.


Be sure you have read, or at least skimmed, the assigned readings for classes through 2/22.

Honor Code Statement

Please include with each part of the assignment the Honor Code pledge or just the word ``pledged'', plus one or more of the following about collaboration and help (as many as apply).1Text in italics is explanatory or something for you to fill in. For written assignments, it should go right after your name and the assignment number; for programming assignments, it should go in comments at the start of your program(s).

Programming Problems

Do the following programming problems. You will end up with at least one code file per problem. Submit your program source (and any other needed files) by sending mail to with each file as an attachment. Please use a subject line that mentions the course and the assignment (e.g., ``csci 1120 hw 5'' or ``LL hw 5''). You can develop your programs on any system that provides the needed functionality, but I will test them on one of the department's Linux machines, so you should probably make sure they work in that environment before turning them in.

  1. (10 points) In CSCI 1320 you probably learned about sorting algorithms and implemented one or more of them. A simple way to test such an algorithm is to generate a sequence of ``random'' numbers, sort them, and check that the result is in ascending order. Sample program sorter-start.c shows how this might be done in C (leaving out the actual sorting). For this problem you will turn in two revisions of this program:

    To repeat: You will turn in two programs, one that just fills in the sort function but sorts the randomly-generated data, and one that gets input from a file and writes to another file.


  2. (10 points) A very simple way to encrypt text is to rotate each alphabetic character N positions. For example, if N is 1, ``abc XYZ 1234'' becomes ``bcd YZA 1234''. (This is obviously not industrial-strength encryption but is good enough to somewhat obscure the plaintext.) Write a C program that implements this scheme. The program should take three command-line arguments: the number of positions to rotate (which for simplicity should be a positive integer), the name of the input file, and the name of the output file. It should print error messages as appropriate (not enough command-line arguments, non-numeric N, input or output file cannot be opened). For valid arguments, it should encrypt the input file and write the result to the output file. To get full credit, your program must encrypt characters as discussed in the hint below.



... apply).1
Credit where credit is due: I based the wording of this list on a posting to a SIGCSE mailing list. SIGCSE is the ACM's Special Interest Group on CS Education.

Berna Massingill