Lab 2 Solution

    • Objectives

The objective of this assignment is to provide you with practice on the use of C++ I/O facilities and string operations. It also provides an introduction to parsing of terminal input and text les, an important skill for almost all programs. You will modify and use this command parser to exercise several of the subsequent assignments.

    • Problem Statement

You will write a command parser that provides a textual input interface to your program, a circuit database program which contains a number of resistors. We do not implement the database here, just the front-end that accepts commands. The parser should take a sequence of commands as input. Each command consists of an operation followed by its arguments. The command and the arguments are separated by one or more spaces. The program should take input from the terminal or a le, parse it, verify that it is correct, and print a response or error message. It will loop, processing input according to the speci cation laid out below as long as input is available.

    • Preparation & Background

Parsing of input from the user and les is critical for most programs. Since content of user input is variable and may or may not be correct, correct program operation requires checking of user input to ensure it conforms to the expected format (\makes sense"). If it does not, an error message should be issued so the program doesn’t \bomb" or run and produce nonsense results. This lab starts with the most basic C++ constructs for reading from a stream which is an object that represents a ow of characters in or out of the program. Streams are a useful abstraction for things like les and the terminal,1 and provide a number of useful functions for extracting values from the underlying source. To start, please read the following background material so you start with some understanding of streams and parsing:

Textbook Chapter 6

Lecture notes on IO and parsing

The use of cin and cout with the IO operators << and >> Documentation on the iostream and stringstream classes2

Also read the spec below (Sec 4) carefully to be sure you understand what you are supposed to

do.


1They also include other things like hardware devices, network connections, pipes between programs, etc - anything that can produce a sequence of characters
    • www.cplusplus.com has a good reference







Page 1 of 9
ECE244    Programming Fundamentals    Fall 2017



    • Speci cations

To receive credit for this lab, you must follow the speci cations below carefully. Where the spec says shall or must (or their negatives), following the instruction is required to receive credit. Any such requirement may be tested by the marking script or by examining the code. If instead is says may or can, these are optional suggestions. The use of should indicates a recommendation; compliance is not speci cally required. However, some of the recommendations may hint at a known-good way to do something or pertain to good programming style. Your code will be marked subjectively for style, so it’s best to take the recommendations unless you have a good reason not to.

Example input and output for the program are provided in Sec 6 for your convenience. They do not cover all parts of the speci cation. You are responsible for making sure your program meets the spec by reading and applying the information below.

4.1    Coding Requirements

    1. The entire program shall be contained in a single source le named Parser.cpp. It should make use of functions to split up the code for readability, and to make it easier to re-use parts of the code in the future.

    2. Input and output must be done using the C++ standard library streams cin and cout.

    3. The stream input operator >> and associated functions such as getline shall be used for all input. C-style IO such as printf and scanf shall not be used.

    4. Strings shall be stored using the C++ library type string, and operations shall be done using its class members, not C-style strings.

    5. C-library string-to-integer conversions (including but not limited to atoi, strtol, etc) shall not be used.

    6. Maximum values shall be stored as #define constants, including MAX NODE NUMBER. For this lab, the MAX NODE NUMBER is 5000.


4.2    Input

All input must be read using the C++ standard input cin. The program shall indicate that it is ready to receive user input by prompting with a greater-than sign followed by a single space (> ) - see Sec 6 for an example. Input shall always be accepted one line at a time, with each line terminated by a newline character3. If there is an error encountered when parsing a line, the program shall print an error message (see Sec 4.3), the line shall be discarded, and processing shall resume at the next line. The program shall continue to accept and process input until an End-Of-File (EOF) condition is received.4

Each line of valid input shall start with a command name, followed by zero or more arguments, each separated by one or more space characters. The number and type of arguments accepted depend on the command. The arguments and their permissible types/ranges are shown below in Table 1.


3A newline character is input by pressing Enter
4EOF is automatically provided when input is redirected from a le or pipe. It can also be entered at the keyboard by pressing Ctrl-D.




Page 2 of 9

ECE244
Programming Fundamentals
Fall 2017








Argument
Description, type, and range









name
A string consisting of any non-whitespace characters, except the string all

which we reserve for special use5 characters


nodeid
Node ID, an integer ranging from 0 to MAX

NODE

NUMBER










resistance
Positive resistance value (type double)



Table 1: Acceptable input arguments


The valid commands, their arguments, and their output if the command and its arguments are all legal are shown below in Table 2. Notice that the last three commands can be run in two ways (depending on their argument): with a speci c node or resistor, or with the keyword all. The program shall verify that the command and arguments are correctly formatted and within range, and that a command is followed by the correct number of arguments, on the same line. The handling of command names shall be case-sensitive. If there is an error, a message shall be displayed as described in Sec 4.3. Otherwise, a successful command produces a single line of output on the C++ standard output, cout, as shown in Table 2. The values in italics in Table 2 must be replaced with the values given by the command argument. Strings must be reproduced exactly as entered. Where nodeids are printed, they shall appear on the order entered in the command. Resistance values shall be printed in xed point format with exactly two decimal places, regardless of the number entered.

Command
Arguments
Output if Command is Valid



insertR
name resistance nodeid nodeid
Inserted: resistor name resistance Ohms nodeid -> nodeid
modifyR
name resistance
Modi ed: resistor name to resistance Ohms
printR
name
Print: resistor name
printR
all
Print: all resistors
printNode
nodeid
Print: node nodeid
printNode
all
Print: all nodes
deleteR
name
Deleted: resistor name
deleteR
all
Deleted: all resistors

Table 2: Valid commands and arguments and their output


4.3    Error Checking

The program must check that the input is valid. It must be able to identify and notify the user of the following input errors, in order of priority. Where multiple errors exist on one input line, only one should be reported: the one that occurs rst as the line is read from left to right. If more than one error could be reported for a single argument in the line, only the error occuring rst in Table reftbl:errors should be reported.

Errors shall cause a message to be printed to cout, consisting of the text \Error: " followed by a single space and the error message from the table below. In the messages, italicized values such as value should be replaced by the value causing the error. Error message output must comply exactly (content, case, and spacing) with the table below to receive credit. There are no trailing spaces following the text.

The program is not required to deal with errors other than those listed in Table 3.




Page 3 of 9

ECE244
Programming Fundamentals
Fall 2017








Error message
Cause








invalid command
The  rst word entered does not match one of the valid commands
invalid argument
The argument is not of the correct type.
For example, a  oating





point number may have been entered instead of an integer nodeid or





a string other than all may have been entered where a nodeid or





all is expected.


negative resistance
The resistance value is strictly less than zero (0.0 is permitted)
node  value  is  out  of  per-
An integer nodeid value has been provided that is out of range
mitted  range  lower

bound-



upper

bound









resistor name cannot be the
A resistor name of all was speci ed to insertR or modifyR
keyword \all"



both terminals of resistor con-
The two nodes to which a resistor connects cannot be the same
nect to node value



too many arguments
More arguments were given than expected for a command
too few arguments
Fewer arguments were given than expected for a command

Table 3: List of errors to be reported, in priority order

    • Helpful Hints

You can check a stream for end-of- le status using the eof member function.

The ignore member function in iostream may be useful to you if you need to ignore the remainder of a line.

To save typing, you can create one or more test les and pipe them to your program. You can create a text le using a text editor (try gedit, gvim, or the NetBeans editor). If your le is called test.txt, you can then send it to your program by typing Parser < test.txt. Building a good suite of test cases is important when developing software.

If you want to look ahead (\peek") at what character would be read next without actually reading it, peek() does that. For instance, if you type \Hello" then each time you run peek() you will get ’H’. If you read a single character, it will return ’H’ but then subseequent calls to peek() will return ’e’.

When interacting with your program from the keyboard, Ctrl-D will send an End-Of-File (EOF) marker.

Reading from cin removes leading whitespace. When reading strings, it discards all whites-pace characters up to the rst non-whitespace character, then returns all non-whitespace characters until it nds another whitespace. For integers (numbers), it skips whitespace and reads to the rst non-digit (0-9) character.

Remember you can use the debugger to pause the program, step through it, and view variables (including strings).

IO manipulators (see header le <iomanip>) can be used to control the appearance of output. You may need at least setprec.



Page 4 of 9
ECE244    Programming Fundamentals    Fall 2017



Double-quotes can be printed to the terminal either as single characters (cout << ’"’) or by escaping them with a slash inside a string (cout << "text n"in quotes n"").
A suggested (but not mandatory) structure for your code would be:

#include <iostream>

#include <sstream>

#include <string>

using namespace std;


int parser() {

string line, command;

// May have some setup code here

getline (cin, line);    // Get a line from standard input

while ( !cin.eof () ) {

    • Put the line in a stringstream for parsing

    • Making a new stringstream for each line so flags etc. are in a known state

stringstream lineStream (line);

lineStream >> command;

if (command == "insertR") {

// parse an insertR command

}

else if ( ... ) {

...

}

getline (cin, line);

} // End input loop until EOF. return 0;
}



    • Examples

6.1    Getting started

The program when    rst started, ready to receive input:

>


Page 5 of 9
ECE244    Programming Fundamentals    Fall 2017



Now the user types a command (ending with Enter) to add a new resistor between nodes 1 and 5, with label of R2 and a resistance of 47.0 Ohms.

> insertR R2 47.0 1 5

To which the program should respond with the message for a successful addition:

> insertR R2 47.0 1 5

Inserted: resistor R2 47.00 Ohms 1 -> 5

6.2    Full session

The following is an example session. Note that the text from the prompt (> ) up to the end of the line is typed by the user, whereas the prompt and line without a prompt are program output.

> insertR R0 100 0 1

Inserted: resistor R0 100.00 Ohms 0 -> 1

> insertR smallres 1.033 3 5

Inserted: resistor smallres 1.03 Ohms 3 -> 5 > insertR newres 3 2 2

Error: both terminals of resistor connect to node 2 > modifyR R0 12

Modified: resistor R0 to 12.00 Ohms

> modifyR R0 -1.5

Error: negative resistance

    • deleteR R0 Deleted: resistor R0

    • deleteR all

Deleted: all resistors

    • printNode 12 Print: node 12

    • printNode 8000

Error: node 8000 is out of permitted range 0-5000 > printR alpha

Print: resistor alpha

> printR

Error: too few arguments

    • printR alpha beta Error: too many arguments

    • Help me!!

Error: invalid command

> modifyR all 33

Error: resistor name cannot be the keyword "all"

>

    • Procedure

Create a sub-directory in your ece244 directory, and set its permissions so no one else can read it.

Create a NetBeans project to build a program called Parser from a single source    le Parser.cpp.

Page 6 of 9
ECE244    Programming Fundamentals    Fall 2017



See the section below on \Compiling your Code" for instructions on how to create a NetBeans project that uses C++ 11, which is required for the assignment. Write and test the program to conform to the speci cations laid out in Sec 4. The hints in Sec 5 may help get you started, and the example sessions in Sec 6 may be used for testing. The ~ece244i/public/exercise command will also be helpful in testing your program, and some of the exercise test cases will be used by the autotester during marking of your assignment. We will not provide all the autotester test cases in exercise, however, so you should create additional test cases yourself and ensure you fully meet the speci cation listed above.

    • Compiling your Code

You must compile your code using the C++ 11 standard. In the rst lab assignment, you edited your .mycshrc le to add the command that enables the use of the correct version of the compilers. If you have not done this edit, please do it before your start with this assignment. Otherwise, there is no need to re-edit the le.

You must also enable the use of the C++ 11 standard when compiling your code. This must happen whether you are using NetBeans or using the command line to build your code. The following are instructions for how to ensure that your are using the C++ 11 standard.

If you are using NeatBeans, start NetBeans either from the desktop menu or from the command line. Create a new project and select \C/C++ Application" for the cetegory of the project, as shown in Figure 1. Click "Next". In the window that follows, enter a name and location for your project. Also make sure that C++11 is selected as shown in Figure 2. If not, use the dropdown menu to select it. Click "Finish". You are now ready to add les to your project. For example, to add a new source le, righ click on "Source Files" under your project and select "Add Existing item ...", as shown in Figure 3.




























Figure 1: Creating a C++ Project in NetBeans



Page 7 of 9
ECE244    Programming Fundamentals    Fall 2017






























Figure 2: Selecting C++ 11 for your project


If you are using the command line to compile your code (instead of NetBeans), you must add the -std=c++11 to your compile commands. For example, if you normally compile a program in the le main.cc, using the command:

g++ -c main.cc

you must now compile it using the command:

g++ -std=c++11 -c main.cc

    • Deliverables

Submit the Parser.cpp le as lab 2 using the command ~ece244i/public/submit 2

The programming style (structure, descriptive variable names, useful comments, consistent indentation, use of functions to avoid repeated code and general readability) shown in your code will be examined and graded as well.












Page 8 of 9
ECE244    Programming Fundamentals    Fall 2017














































Figure 3: Adding Files to your project






















Page 9 of 9