Computer Science 202
Systems Programming Concepts Using C
Lab 2 - Math Trick
Write a C program using the GNU C Compiler (gcc) that will interact
with the user to perform a simple math trick.
The math trick works as follows:
| 1. Ask the user to enter a positive integer.
| 2. Determine the sum of the digits in the number.
| 3. Subtract the sum from the original number.
| 4. Ask the user to re-arrange the digits.
| 5. Add 25 to the number.
| 6. Ask the user to remove one of the non-zero digits from the number.
| 7. Determine the sum of the digits in the number.
| 8. Subtract 7 from the sum of the digits.
| 9. Subtract the result from the next highest multiple of 9.
|| 9 - 6 = 3
The trick is that the final value (3 in the above case) is the digit
that the user eliminated from the number. That's it. (Sorry if you
You are to write a C program that performs the above trick. A portion of
your grade will be based in the quality of your interactive program.
Before the end of class on 2nd Tuesday you must demonstrate to
your instructor that your program successfully adds up the digits of
The following must be delivered to your instructor via text-only
email no later than midnight of 3rd Monday January 19, 1998.
In addition, you must deliver to the instructor at the start of class (Lab) on
3rd Tuesday, January 20, 1998 the following:
- Source code for your program.
- A printed copy of your source code.
- An example of an interactive session you used to test your program.
- When you create your C program give it a name with a .c extension,
prog1.c or trick.c for example.
- To compile your C program use the gcc command from the command line,
for example: gcc prog1.c
- If your program compiles successfully a file named a.out will
- To run your program simply type a.out at the command line.
- Other compilation options:
- Use the standard input and output streams for your I/O.
- Proper use of programming style is required. A correctly running
program with gross style violations can be worth as little as 25\% of the
- Programs are graded as follows: The mailed source is compiled, with all
warning messages enabled. A program which does not compile is worth zero
points. If it compiles, it is run on your test data. It is also run on
the instructors data. At this point, a raw grade (range 0-50) is assigned.
Your source code is then examined for adherence to programming standards. Your
final grade is then your raw grade minus any deductions for style.
- You are expected to do all of your own code writing, but you may help
others with algorithm design and debugging of already written code. If, when
assisting others, you write statements that resemble C code, you are
probably providing too much help.