CS 215 Fundamentals of Programming II Fall 2017 Project 7. Morse Code. 30 points. Out: November 20, 2017 Due: December 4, 2017 (Monday) a n m

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1 CS 215 Fundamentals of Programming II Fall 2017 Project 7 30 points Out: November 20, 2017 Due: December 4, 2017 (Monday) This project is to build a Morse code tree and use it to encode and decode messages. Morse Code Morse code was developed for sending messages across telegraphic wires. The code consists of patterns of short and long elements often called dots and dashes, respectively. Each letter, digit, and symbol is assigned a specific pattern of dots and dashes. The Morse code can be represented using a binary tree where the left branches represent a dot and the right branches represent a dash. For example, here is a portion of the Morse code tree: e t a n m r g The code for each character is a string formed by appending a '.' when taking a left branch and a '-' for a right branch when traversing the path from the root to the node containing the letter. In the codetree above, the code for 'r' is ".." (left, right, left), the code for 'm' is " " (right, right), and the code for 'a' is ". " (left, right). A message is encoded by giving a sequence of codes for the letters in the message. Since Morse code does not have a prefix property (that is, a sequence of elements that represents one character may be a prefix of a longer sequence for some other character, e.g., the codes for 'm' and 'g'), there is a space between each character code. For example, the Morse code for the message "ram" is "... ", which is formed by listing the codes for 'r', 'a', and 'm' separated by spaces. Since a space is used to separate character codes, an actual space between words will be represented in the code as ' '. Likewise a newline will be represented in the code as " ". (In actual Morse code, words and sentences are separated by longer silences than the silence between characters, but we do not want to count spaces for this project.) Thus if the message "garment ten" is followed by a newline, our Morse code for the message would be For this project, you will be given codefiles containing the Morse code for lowercase alphabetic characters. Your assignment is to write a MorseTree class (specification given below) that can read a codefile and construct a codetree for use in encoding and decoding messages, and write a (main) program to encode and decode messages using a MorseTree object. 11/20/2017 Page 1 of 7 D. Hwang

2 Specification for TreeNode struct The TreeNode struct is used to implement a node of the Morse codetree. The definition should be placed inside a private section in the MorseTree class definition in the morse.h header file, similarly to the Term struct used in Project 5 except it is in lined instead of in a separate file. Data Attributes Object Type Name letter char data link to the left child TreeNode * lchild link to the right child TreeNode * rchild Operations Explict value constructor with default arguments initializes the attributes of the TreeNode struct. This function is to be in lined in the struct definition. Objects Default argument Type Movement Name letter '*' char received initial_letter link to the left child nullptr TreeNode * received initial_lchild link to the right child nullptr TreeNode * received initial_rchild Specifications for MorseTree Class Attributes There is only one attribute of this class, a single TreeNode pointer variable that points to the root of the constructed codetree. Operations (Note: there is no default constructor for this class. It does not make sense to be able to create an empty codetree.) Explicit value constructor builds the codetree from an input stream connected to a codefile. Assumes that the stream is valid. input stream connected to codefile istream received & passed back code_file 11/20/2017 Page 2 of 7 D. Hwang

3 The codefile will consist of an integer n, followed by n lines of the form letter code where code is the Morse encoding for letter. The constructor is to read the codefile and build the codetree. For example, the codefile for the codetree shown above would be: 7 a. e. g. m n. r.. t The basic algorithm is to read each letter (as a character) and its code (as a string) and use the code to traverse the tree (starting with the root) as one would do when decoding. If an interior node does not exist, create it and continue. When the end of the code is reached, you are at the node that stores the letter. Copy constructor creates a copy of the original MorseTree using the copy_tree private member function described next. original tree MorseTree received source copy_tree private recursive helper function that copies a binary tree and returns the root of the copy. root of tree to copy TreeNode* received source_root root of copy TreeNode* returned copy_root Copying a tree given a pointer to its root is a post order traversal: make copies of the left and right subtrees, then make a new root node for the copy that points to them. Destructor deletes MorseTree nodes using the delete_tree private member function described next. no objects delete_tree private recursive helper function to delete binary tree nodes. root of tree to delete TreeNode* received source_root Deleting a tree given a pointer to its root is a post order traversal: delete the left and right subtrees, then delete the root node. 11/20/2017 Page 3 of 7 D. Hwang

4 operator= assignment operator, make this MorseTree a copy of the source MorseTree, returns a reference to this object. This function must be implemented using the copy and swap technique. original tree MorseTree received source this tree MorseTree & returned *this write writes out the codetree "sideways" to an output stream using the private overloaded recursive write_tree helper function described next. write_tree private recursive helper function to write out a tree to an output stream using an RNL traversal (right, visit node, left). Each node value should be written on a separate line with (8*depth) number of spaces before it (where the root value starts at depth 0). Empty trees do not create any output. root of tree to write TreeNode * received local_root depth of node int received depth encode encodes message from an input stream, writing results to an output stream, using char_to_code private member function described next. Assumes the streams are valid. input stream connected to message file istream received & passed back message_file The basic algorithm for this function is to repeatedly read a character (including spaces and newlines, so use get()) from the input stream, encode it using helper function char_to_code. If the resulting code is not whitespace, then write the encoding to the output stream. Note there is a space between each encoding, but there is no space at the end. In order for the resulting file to be a proper text file, the output file must end with a newline after all the input characters have been encoded. You may assume that the message file contains only the characters in the codetree, spaces, and newlines, and ignore any characters that do not encode properly. However, you may want to display an error message if no encoding is found for a read character stating that the character is being ignored. 11/20/2017 Page 4 of 7 D. Hwang

5 char_to_code private recursive helper function to find an encoding from the codetree. character to encode char received ch node of tree being traversed TreeNode* received t path constructed so far string received path_so_far encoding for character string returned code The basic algorithm for this function is to build a path (in path_so_far by concatenating a. or as appropriate) as the function traverses the codetree. When the character is found, return the path. Otherwise, if an empty tree is reached without finding the character, this was not the correct path and return the empty string. Note: concatenating multiple empty strings results in an empty string. decode decodes message from an input stream, writing results to an output stream. Note: this function is not recursive. Assumes the streams are valid. input stream connected to encoded message file istream received & passed back message_file The basic algorithm for this function is to read in a character code (as a word, so use >> ) and use it to traverse the codetree starting at the root. When the end of the character code is reached, write out the letter in the node, then start over again with the next character code. In addition to character codes, there may be "codes" of ' ' and " " representing a space and a newline, respectively, that are to be decoded to those characters. You may assume that the encoded message file contains only valid input, and ignore any other inputs. However, you may want to display an error message if invalid characters or character codes are found in the input stream stating they are being ignored. (Note that the ending newline of the original plaintext file should be encoded, so the result file of decoding will have the required ending newline automatically.) Assignment (20 points) Write the implementation of the MorseTree class. The TreeNode struct definition with constructor and the MorseTree class definition should be put in header file morse.h with suitable compilation guards. The implementations of the MorseTree class functions should be put in source file morse.cpp. (10 points) Write a (main) program in file coder.cpp that has one command line argument, the name of a codefile. All appropriate error checking must be completed. The program should construct a MorseTree object using the given codefile, then display the constructed codetree to the screen. Then the program should enter a menu driven loop that asks the user if they want to encode, decode or quit. For encode and decode, the program should ask for an input file name and an output filename, then do the appropriate action reading in from the input file and sending the output to the output file. 11/20/2017 Page 5 of 7 D. Hwang

6 Two codefiles will be given in /home/hwang/cs215/project7 on csserver. The file samplecodefile.dat will be the partial Morse code used in the examples above, thus suitable for preliminary testing of your class. The file morse.dat will contain the full Morse code for the lowercase Latin alphabet. (A link to a picture of the entire Morse code tree is available at the course webpage.) You will have to write your own sample input files. Note that when the encode and decode functions are working, you should be able to send the output of the encode function into the decode function and get back your original plaintext message (and vice versa). You can use the diff command to see if two files are the same. You must submit a makefile Makefile that creates an executable file named coder for your project. It should conform to the examples demonstrated in class. REMINDER: Your project must compile for it to be graded. Submissions that do not compile will receive a score of 0. Submissions that do not substantially work also will receive a score of 0. Follow the guidelines in the C++ Programming Style Guideline handout. As stated in the syllabus, part of the grade on a programming project depends on how well you adhere to the guidelines. The grader will look at your code listing and grade it according to the guidelines. What to submit Electronically submit a tarfile containing Makefile, morse.h, morse.cpp, and coder.cpp as explained in the handout Submission Instructions for CS 215. Do not submit object files, or executable files. The submission system will accept submissions no earlier than Wednesday, November 29. Note: the submission system will run a specific driver program to test your MorseTree class operations, not including the copy constructor, destructor, and assignment operator. It will only compile the menu driven coder program and check for the appropriately named coder executable file. It will not run the coder program. Example Run user@csserver:~/cs215/project7$ more samplemessage.plaintext garment ten user@csserver:~/cs215/project7$./coder samplecodefile.dat m g t n * a r e Please choose one of: E Encode a message D Decode a message Q Quit the program Enter your choice: e Enter the name of a plaintext message file: samplemessage.plaintext Enter name of output file: samplemessage.encoded Please choose one of: E Encode a message 11/20/2017 Page 6 of 7 D. Hwang

7 D Decode a message Q Quit the program Enter your choice: d Enter the name of an encoded message file: samplemessage.encoded Enter name of output file: samplemessage.recovered Please choose one of: E Encode a message D Decode a message Q Quit the program Enter your choice: q user@csserver:~/cs215/project7$ more samplemessage.encoded user@csserver:~/cs215/project7$ more samplemessage.recovered garment ten user@csserver:~/cs215/project7$ 11/20/2017 Page 7 of 7 D. Hwang