辅导案例-CSCI-1200
CSCI-1200 Data Structures — Fall 2019
Homework 1 — Text Justification
Before starting this homework, make sure you have read and understood the “Academic Integrity Policy”.
This homework assignment is a programming exercise involving simple text manipulation to format input
text into a framed column with a specified width. You will work with command line arguments, file input
and output, and the C++ Standard Template Library string and vector classes. Please read the entire
assignment before starting to program. When you are ready to begin, create a subdirectory for homeworks
within your main Data Structures course directory and within that directory create a subdirectory hw1 for
this assignment.
Your program will read words from an input file and greedily pack the words one at a time onto each line,
making sure not to exceed the specified width. Your program will support three different methods for dealing
with any extra, unused space on each line. The first, flush left, simply positions each word as far to the left as
possible, leaving a gap of spaces (if any) on the right. The second, flush right, does the opposite, pushing all
the words to the right, and puts the extra spaces on the left. In the final mode, full justify, the extra spaces
are distributed evenly between the words. If the number of extra spaces on the line do not divide evenly into
those “between” slots, the slots on the left will be assigned more spaces that the slots on the right.
Let’s look at a simple example. Here is a sample input file, named example.txt:
Here is an example of text justification.
And here’s the output produced for that input file for the three different justification modes, for the specified
text width of 16:
flush left flush right full justify
--------------------
| Here is an |
| example of text |
| justification. |
--------------------
--------------------
| Here is an |
| example of text |
| justification. |
--------------------
--------------------
| Here is an |
| example of text |
| justification. |
--------------------
First note that the output includes a simple ascii art line box drawn around the text, but those characters
do not count towards the specified line width of the text. In other words, each line of final output is actually
4 characters longer, in this example, 20 total characters. Notice that the same words appear on each line
in all three cases. The only difference is where the “extra” spaces appear. The top line has 6 extra spaces
(16 - # of characters in “Here is an” = 6). In full justify mode, these spaces are evenly divided into the 2
slots between the 3 words. The second line has 1 extra space (16 - # of characters in “example of text”
= 1). This extra space is assigned to the leftmost of the two slots on the second line. Also note a typical
convention for full justify formatting: The last line of a block of text formatted with full justify is not forced
to stretch all the way to the right edge. No extra space is inserted between words on the last line – it should
be flush left justified only.
File I/O
You will read the words to format from an input text file. You should not make any assumptions about the
formatting of this file, except that the words will be separated by at least one whitespace character. Remember
that whitespace characters include spaces, tabs, and newlines. Any punctuation in the file (including periods,
commas, apostrophes, etc.) should be treated as part of the word if it is not separated from the word by
spaces. The basic iostream string input operator, >>, will work perfectly for this assignment. The output of
your program will be written to a file, and should follow the specifications in this handout and match our
examples. Reading and writing files in C++ is very similar to std::cin and std::cout. See examples of
STL file streams on the course webpage “Helpful C++ Programming Information”.
Command Line Arguments
Your program will expect 4 command line arguments. The first is the name of the input file. The second is
the name of the output file. The third argument is an integer that specifies the width of the text column. The
fourth argument will be a string (flush_left, flush_right, or full_justify) specifying which formatting
mode should be used. Here are examples of valid command lines for your program:
./justify.exe example.txt example_16_flush_left.txt 16 flush_left
./justify.exe example.txt example_16_flush_right.txt 16 flush_right
./justify.exe example.txt example_16_full_justify.txt 16 full_justify
You should implement very simple error checking to ensure that 4 arguments are provided and that the
input and output file streams are successfully opened. You should also check that the values for the third
and fourth arguments are valid. Your program should exit gracefully with a useful error message sent to
std::cerr if there is a problem with the arguments.
You must follow the specifications for the command line, input file, and output file exactly to ensure you
receive full credit from the Submitty homework submission autograder. We have provided sample input &
output files on the course website. Examples of using command line arguments can be found on the course
webpage: “Helpful C++ Programming Information”.
Corner Cases
So now you understand the core requirements for this assignment, but you may already have thought of a
few problem cases. For example, how should the program full justify a line that contains just a single word?
There are no available slots between words to use to insert the extra spaces. In this case your program
should simply left justify the line. Another question you might ask is what to do if one of the words in the
file is (by itself!) wider than the width of the column? In your initial coding and testing we recommend you
assume that this will never happen. This solution will be worth nearly full credit. To receive full credit on
the assignment your program should handle this case by splitting the word and inserting a hyphen. Note
that we do not expect you to properly split the words between syllables, as that would require a database
of English words and syllables. If you think of other corner cases as you work on the assignment, propose
reasonable ways to handle those situations. If those solutions are overly complex or tricky, you do not need
to tackle the implementation, but you should write up your thoughts in your README.txt for the grader
to read.
Extra Credit
Once the fundamental requirements of the assignment are completed, you may implement some fun extensions
to earn a few points of extra credit. Rather than formatting the text inside a simple rectangular column,
output the text inside of a triangular, trapezoidal, or even circular frame. Document your extensions in your
README.txt file and include a sample command line and sample output file with the results.
Submission Details
Use good coding style when you design and implement your program. Organize your program into functions:
don’t put all the code in main! Be sure to read the “Good Programming Practices” as you put the finishing
touches on your solution. Be sure to make up new test cases to fully debug your program and don’t forget
to comment your code! Use the provided template README.txt file for notes you want the grader to read.
You must do this assignment on your own, as described in the “Collaboration Policy & Academic Integrity”
handout. If you did discuss the problem or error messages, etc. with anyone, please list their names in your
README.txt file. Prepare and submit your assignment as instructed on the course webpage. Please ask a TA
if you need help preparing your assignment for submission or if you have difficulty writing portable code.
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