CS 270
Number Conversion in C
Programming Assignment P1: CS270 Computer Organization

Programming Assignment P1 - Number Conversion

This assignment has four objectives:
  1. To learn how to to compile multiple C files into an executable program.
  2. To demonstrate that many of the Java programming constructs you learned are valid in C. (Java and C++ syntax were based on C).
  3. To learn how to convert between human readable numeric values and internal numeric values and vice-versa.
  4. To become comfortable working in various number bases.
  5. To learn a little about C pointers.
  6. To practice recursion.

First read the Getting Started and Completing the Code sections below and then study the documentation for numconv.h in the Files tab to understand the details of the assignment. In addition, these two references provide additional information:

Getting Started

Perform the following steps
  1. Create a directory for this assignment. A general scheme might be to have a directory for each CS class you are taking and beneath that, a directory for each assignment. The name of the directory is arbitrary, but you may find it useful to name it for the assignment (e.g. P1).
  2. Copy the three files below into this directory. It is easiest to right click on the link, and do a Save Target As.. for each of the files.
  3. Open a terminal and make sure you are in the directory you created in step 1. The cd command can be used for this.
  4. In the terminal type the following command to build the executable:
        c11 -g -Wall numconv.c testConv.c -o testConv
    This command performs both the compilation and linking steps. You must run this command every time you make a change to your file.

  5. In the terminal type ./testConv and read how to run the the program. There are 6 functions which you must implement. The testConv program will call one of your functions depending on the arguments that you pass. For example, if you type ./testConv i2c 2 6, your int2char(...) function will be called with the parameters 2 and 6. This allows you to test one function at a time.

You now have a functioning program. All the commands (i2c, c2i, etc.) do something. However, none will produce correct results at this point.

Completing the Code

Before attempting to write any of the functions of numconv.c, study the documentation found in the Files tab. You are especially interested in the documentation for numconv.h. Notice that this file contains function declarations. For example:

    int char2int (int radix, char digit);
A declaration lacks a function body. It simply tells the compiler the name of the function and the parameters that it takes. The actual function body is defined in numconv.c. This is a common practice in C: we have a .h file that declares the functions just to tell the compiler that they exist, and then we have a .c file that defines them (specifies what they do). In this exercise, numconv.h is included by both numconv.c and testConv.c. That way, testConv.c knows about the existence of the functions defined in numconv.c.

Plan what you need to do before writing code!

The best way to complete the code is to follow a write/compile/test sequence. Do not attempt to write everything at once. Rather, choose one function and do the following steps.

  1. Write some/all of one function in numconv.c using your favorite editor.
  2. Save your changes and recompile numconv.c using the command shown above. You may find it convenient to work with both a terminal and editor window at the same time.
  3. Repeat steps 1 and 2 until there are no errors or warnings.
  4. Test the function you have been working on. Do not attempt to move on until you complete and thoroughly test a function. You will find that the function int2char() is called in the int2ascii() function and that char2int() is useful in ascii2int(). Therefore, you might write the functions in the following order:
    1. int2char()
    2. char2int()
    3. divRem()
    4. ascii2int()
    5. int2ascii() make sure this function does not print leading zeroes!
    6. frac2double() [Extra Credit]
  5. Repeat steps 1 thru 4 for the remaining functions.

The divRem() function

Remember how we used a pointer in P1 to return a value from a function? The divRem() function computes the quotient and remainder and returns both to the caller using two pointers. The result is that the function is able to return multiple values to the caller. The caller passes pointers to the addresses where it wants the results stored and the function uses the dereference operator to store the values. This is the same way the functions in the P1 assignment used to return the area of a figure. Review your notes from class and study how pointers are used in testConv.c.

You may implement this function however you want, including using the C operators for division and modulus (/ %). However, a good exercise is to implement it using repeated subtraction.


This program is more about thinking than it is about writing code. Here are the lengths in lines of code for our solution (including blank lines and comments): Take these as guidelines, not specifications. Depending on your style, you may get more or fewer lines of code.

Refer to the following videos where Andres talks about the functions and gives you tips:


Your program must meet the following specifications:

Grading Criteria

Submit the single file numconv.c to the Checkin tab on the course website, as you were shown in the recitation.
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