Description
This week’s assignment will have you write a program that performs addition of very large numbers via
arrays. Also, this assignment will give you practice creating a multiple-file program whose parts can be
compiled separately. Feel free to work in pairs and ask for help early.
You may recall performing long addition by hand:
You add the digits in the ones column, carrying the one if the sum is ten or more. Then moving to the
tens column and repeating the process until you’re done.
We have discussed how integers have a maximum value they can represent, which isn’t very large
(2,147,483,647). We can represent a much larger number in an array through, if each digit is stored in
one of the array’s elements. As you can see on the left below, the numbers may have different lengths,
and that can make it difficult to align the columns for ones, tens, etc. But, as you see on the right, if we
reverse the digits in the numbers, then the ones column is at index 0, the tens index 1, etc. This is
visually backwards, but we are now able to perform long addition using the matching columns.
0 1 2
5 7 8
0 1 2 3
1 7 1 3
0 1 2
8 7 5
0 1 2 3
3 1 7 1
Your program will consist of three files:
• A header file named bigint.h
• An implementation file for the header file, named bigint.cpp
• A main program file named main.cpp
The main program, main.cpp, has been provided for you. You will use this file as-is, except for the
addition of your preamble.
The bigint.h header file must contain the prototypes of the three functions described next. You are
provided the prologues for the three functions, which you use to implement the behavior of each. Within
the prologues you will find the function name, a description of what it does, pre- and post-conditions,
CSCI 136 Supervised Programming Lab
Lab Assignment #6
Fall 2014 Page 2
and the return value. Also, you’ll find each parameter explained, along with whether it acts as an input
or input and output together:
/** addBigIntegers(num1, num1_size, num2, num2_size, result_num)
* @desc adds the number represented by the arrays using long addition,
* placing the result into result_array
* @param int num1[] [in/out] – a number stored as an array
* @param int num1_size [in] – the # of digits in the first number
* @param int num2[] [in/out] – a second number stored as an array
* @param int num2_size [in] – the # of digits in the second number
* @param int result_num[] [in/out] – an array to store the result number
* @pre declared size of result_num is max(num1_size, num2_size)
* @post the number representing the sum of num1 and num2 is stored in
* the result_num array
* @post the digits in num1, num2 and result_num are in proper order
* @return the number of digits in result_num array
**/
/** printBigInteger(outputstream, num, size)
* @desc prints the number represented by the digits in the num array
* to the output stream
* @param ostream & outputstream [in/out] – the stream to write to
* @param int num[] [in/out] – the number to print as an array
* @param int size [in] – the size of the array
* @pre outputstream is open for writing
* @post the digits in num have been written to the output stream
* @return none
**/
/** reverseArray(array, size)
* @desc reverses the elements in an array
* @param int array[] [in/out] – the array to reverse the elements of
* @param int size [in] – the used size of the array
* @pre none
* @post the first element is now the last and the last is now the first;
* the second element is now the second to last…
* @return none
**/
The file bigint.cpp must contain the definitions for the function prototypes in the header file.
It is your task to create the header and implementation files and then write the correct function
prototypes and definitions to make the main work.
I recommend you create the header file first, adding the prototypes. Then, work on the implementation
file. I strongly urge you to work out the algorithm needed for the addBigIntegers function, before you
try to write any of the code.
CSCI 136 Supervised Programming Lab
Lab Assignment #6
Fall 2014 Page 3
Submitting your work
Each of your source code files must have a preamble at the top (see the programming rules and
guidelines document in Blackboard for more on the preamble).
Make sure you are in the folder with your source code files (use the ls command) and then run the
following to create a zip archive of them:
$ mkdir lastname_firstname_lab07
$ cp main.cpp lastname_firstname_lab07/main.cpp
$ cp bigint.h lastname_firstname_lab07/bigint.h
$ cp bigint.cpp lastname_firstname_lab07/bigint.cpp
$ zip –r lastname_firstname_lab07.zip lastname_firstname_lab07/
You’ll need to change lastname and firstname to your actual last and first names (use lowercase
letters) in the steps above. Once you have your zipfile, you can use that file as your submission for the
assignment in Blackboard.
If you are working in pairs, then you should have both of your names included as comments in the
source code file’s preamble (see the programming rules and guidelines document in Blackboard for
more on the preamble). Also, write both your names to the notes section in the submission form when
submitting to Blackboard.
