Test 2: Class Section A

Thursday 4th May 1995

This test will be made up of three parts:

1. Debugging, running and testing a provided program.

2. Making use of the above program in the development of a new program and then testing this extensively.

3. Making minor alterations to the original program in order to improve the quality of the code, and/or to add additional functionality.

Note that marks will be awarded purely on the quality of the content of the final report. Therefore, at all stages of the test, please describe plans, algorithms, problems encountered, tests carried out and, when the required tasks have been completed, describe any conclusions drawn from the exercise.

Part 1 (40%)

The program ENCODE.C in supposed to take in five characters from the keyboard and encrypt them by:

(i) reversing their order,

(ii) shifting the first character by one, the second by two and so on.

The resultant code is then printed to the screen. There are, however, a number of errors in the program.

(a) Present a reformatted version of this program which demonstrates satisfactory practice for spacing, line breaking and indentation. Add comments where relevant to improve the understandability of the program.

(b) Correct any compiler / linker errors. In the case of compiler warnings, either resolve them or explain why they can be ignored.

(c) When the program compiles successfully, run it and establish the presence of any runtime errors. Correct these.

(d) Test the program extensively to ensure correct operation.

Part 2 (40%)

Write a program to decrypt the output of the above encoder. You may either do this through reuse of code from the original ENCODE.C program, or you may create your own version of the program. However, the following guidelines must be followed:

1. The program must be divided into functions.

2. No global variables - all variables must be local to some function. Use parameter passing and/or return values where appropriate to exchange information between functions.

3. The program should not be restricted to decoding five characters only - any number of characters (up to 50) may be entered and completion of entry should be signified by EOF.

4. The program should demonstrate good coding practices with regard to spacing, comments etc.

Test this program rigorously - this may be done in conjunction with the original encoder. Describe all results.

Part 3 (20%)

It is required to extend the original encoder so that it repeatedly takes in five characters and prints the equivalent code. It should continue doing so until an EOF is encountered, at which stage the program should terminate. Test this program rigorously and detail all results.