Answered Essay: s are clogged with the dozens of spam email messages they receive each

Introduction

Jee-mail, a small email service provider, has been receiving complaints from customers claiming that their inboxes are clogged with the dozens of spam email messages they receive each day. Consequently, Jee-mail has contracted with the Fruggle Corporation to design and build a spam detection system. Of course, since Fruggle gets all of its labor by exploiting El Camino students, you’ll be doing all of the programming.

Given one or more email messages, your program will have to classify each one as either spam or legitimate. Jee-mail wants you to build a point-based anti-spam system. Your program is to look for certain suspicious features in the email, such as frequent use of exclamation points (!), use of words like FREE, or excessive use of uppercase letters. Each time such a suspicious feature is found, you increase a score that indicates how suspicious an email is. If an email’s score exceeds 100 points, then it is classified as spam; otherwise, it is deemed legitimate. The detailed rules for scoring a message are in the Spam Rules section below.

Sample Transcript

Here is a sample transcript of the program, with boldface text representing the user’s input.

Enter the subject line of the email: MAKE MONEY FAST XTFWAQQQ
Enter the body of the email.  Press Enter on an empty line to finish.
THIS IS YOUR CHANCE TO MAKE lots of moolah!
CLICK ON www.lotsofmoolah.com FOR MORE INFORMATION!
        ← the user just hit the enter key on this line
This email is classified as spam, because its spam score is 115.
Would you like to classify another email (y or n)? Quit
Please enter y or n.
Would you like to classify another email (y or n)? Y
Please enter y or n.
Would you like to classify another email (y or n)? y
Enter the subject line of the email: hi mom
Enter the body of the email.  Press Enter on an empty line to finish.
Hi mom,
I hope you're doing OK.  My CS class is great, but the instructor is WEIRD!
I love you!
        ← the user just hit the enter key on this line
This email is classified as legitimate, because its spam score is 0.
Would you like to classify another email (y or n)? n

Number of spam messages: 1
Number of legitimate messages: 1

Input and Output Specification

The first line that your program must print out is exactly this (with one space after the colon):

Enter the subject line of the email:

Your program must then read the subject line the user types in. (It is not an error if the subject line is the empty string.) After that, your program must print out exactly this line:

Enter the body of the email.  Press Enter on an empty line to finish.

Your program must then read the message body lines the user types in. The message body consists of zero or more lines. After your program reads an empty line, which indicates the end of the message, it must print out exactly one of these two messages, depending on whether applying the spam rules classified the message as spam or not:

This email is classified as spam, because its spam score is number.

or

This email is classified as legitimate, because its spam score is number.

In these messages, number is to be replaced by the appropriate spam score, such as 115, or 0, or 5.

After printing the classification message, your program must print exactly this (with one space after the question mark):

Would you like to classify another email (y or n)?

Your program must then read the line the user types in. If the user types only a lowercase y, the program must process another email, starting with the step where it prints the prompt for the subject line of the email.

If instead, the user types only a lowercase n, the program must print an empty line, then print the following two lines, then terminate:

Number of spam messages: number
Number of legitimate messages: number

In these messages, the first number is the number of messages that were classified as spam, and the second is the number that were classified as legitimate.

If the user types anything other than a single lowercase y or n in response to the question, the program must print out exactly the line:

Please enter y or n.

and repeat the prompt about classifying another email. It must repeatedly prompt the user until y or n is selected.

Spam Rules

The Jee-mail spam experts have come up with five rules, each of which can contribute some points to the spam score of a message. If the total spam score for the message is more than 100, the message is classified as spam; otherwise, it is considered a legitimate message. You must use only these five rules; do not improvise and make up your own. (Save that for when you start your own competing spam filter company.)

First, some definitions: a word in a string is a contiguous sequence of letters delimited either by non-letter characters or by the start or the end of the string. A letter may be upper- or lowercase. As an example, the string It’s like the old-fashioned 1980s! has these seven words:  It s like the old fashioned s. A consonant is a letter other than one of these ten: aeiouAEIOU.

Here are the five rules. The first three relate to the subject line of the email, while the last two are concerned with the body of the message.

If the subject line has at least one word, and more than 90% of the words in the subject line consist of only uppercase letters, then add 30 points to the spam score. For example, a subject line of

GET A DIPLOMA FREE!!

meets this criterion.

If the last word of the subject line contains more than 3 consecutive consonants, then add 40 points to the spam score. Spammers often place random words at the end of a subject line to confuse some anti-spam software; this rules detects many of those random words. For example, this subject line earns the 40 point addition to the score:

This stock is going up, up, up!  mqafrpxo!

If the subject line contains 3 or more contiguous exclamation points, then add 20 points to the spam score. This subject line qualifies for the 20 points, for example:

Make money fast!!!  No experience necessary!!!!!

If the body of the message has at least one word, and more than 50% of the words making up the body of the email consist entirely of uppercase letters, then add 40 points to the score. For example, this email:

Subject:  Greetings from your good friend
Body:
        THIS IS YOUR CHANCE TO MAKE lots of moolah!
        GO TO www.lotsofmoolah.com FOR MORE INFORMATION!

earns the 40 points because there are 17 words in the body of the email, 11 of which (64.7%) are entirely uppercase.

Each time one of the following special words is found in the body of the email, add 5 points to the spam score for that message. The letters in these words may be in either case (e.g., SeX is the same as sex):

buy
cheap
click
diploma
enlarge
free
lonely
money
now
offer
only
pills
sex

For example, this message would score 35 points, 5 for each of the words indicated in boldface:

Subject:  Looking for cheap tickets?
Body:
        You can find cheap! tickets ONLY on our website.  Save money with this
        great OfFeR!!  Don't be a cheapskate.  Click now for this offer!

Notice that the “cheap” in the subject line is ignored by this rule, as is the word “cheapskate” in the second line of the body.

Functions You Must Write

We know that this will be the most complex program that many of you will have written in your programming careers to date, so we will make it easier for you by decomposing the problem for you.

To get full credit for this project, you must implement all of the following functions, using the exact function names, parameters types, and return types shown in this specification. The functions must not use any global variables whose values may change. (Global constants are all right.) In addition to testing your program as a whole, we will also test each of the following functions separately. That way, if your program doesn’t work overall but you correctly implemented some of the functions, you’ll still get some credit.

The functions you must implement are

        getFirstWord
        getLastWord
        extractWord
        isUppercase
        makeUppercase
        hasMultipleExclamations
        isGibberishWord

Your solution should use these functions where appropriate (although you might not use every one of them). One reason is to help you get partial credit in the case where most of your program is correct, but a few of the function implementations are incorrect.

To help you implement these functions, you might choose to write additional functions as well. While we won’t test those additional functions separately, using them may help you structure your program more readably. If you find it helpful, you might have some of these seven required functions call other functions in that list.

When you turn in your solution, none of these seven required functions, nor any functions that they call, may read any input from cin or write any output to cout. (Of course, during development, you may have them write whatever you like to help you debug.) If you want to print things out for debugging purposes, write to cerr instead of cout.  cerr is the standard error destination; items written to it by default go to the screen. When we test your program, we will cause everything written to cerr to be discarded instead — we will never see that output, so you may leave those debugging output statements in your program if you wish.

string getFirstWord(string text)

This function returns the first word in the string variable text. If text has no words, this function returns the empty string (i.e. “”). Here is an incomplete test driver for this function:

        void test()
        {
              // This writes "Hello"
            cerr << getFirstWord("!!Hello, Fred") << endl;

              // This writes "greetings 9"
            string msg = "greetings, mom, how are you?";
            string result = getFirstWord(msg);
            cerr << result << " " << result.size() << endl;

              // This writes "0"
            string s = getFirstWord(" $@#%!!");
            cerr << s.size() << endl;
        }

Hint: The string substr function may be of use in the implementation of this function.

string getLastWord(string text)

This function returns the last word in the string variable text. If text has no words, this function returns the empty string (i.e. “”). As an example, getLastWord(“MAKE MONEY FAST!!”) returns “FAST”.

Hint: The string substr function may be of use in the implementation of this function.

string extractWord(string& text)

This function returns the first word in the string that text is a reference to. If that string has no words, this function returns the empty string.

This function also modifies the string that text refers to. If that string has no words, then this function sets text to the empty string. Otherwise, it removes from text the first word of text and all non-letters preceding that first word. Here is an incomplete test driver:

        void test()
        {
            string s = "***AMAZING!*** Do it, now!!";
            string w = extractWord(s);
              // This writes "AMAZING" and "!*** Do it, now!!"
            cerr << w << endl << s << endl;

            w = extractWord(s);
              // This writes "Do" and " it, now!!" (space before "it")
            cerr << w << endl << s << endl;

            w = extractWord(s);
              // This writes "it" and ", now!!"
            cerr << w << endl << s << endl;

            w = extractWord(s);
              // This writes "now" and "!!"
            cerr << w << endl << s << endl;

            w = extractWord(s);
              // This writes "" and "" (both empty strings)
            cerr << w << endl << s << endl;
        }

Hint: The string substr function may be of use in the implementation of this function.

bool isUppercase(string text)

This function returns true if and only if every letter in the string text is uppercase. (For a string with no letters, this means the function returns true.) Non-letter characters in the string text, if any, have no effect on the result of this function.

string makeUppercase(string text)

This function returns a new string identical to the value of the string text, except that each lowercase letter of text appears as its uppercase equivalent in the result string. For example, makeUppercase(“Earn *big* MONEY at home!!”) returns “EARN *BIG* MONEY AT HOME!!”.

bool hasMultipleExclamations(string text)

This function returns true if and only if the string text contains three consecutive exclamation marks. For example, it returns true for the strings “Wow!!!” and “Congrats!!!! Good luck”, and false for the strings”W!I!N!” and “!! !”.

bool isGibberishWord(string text)

This function returns true if and only if the string text contains more than three consecutive consonants. For example, it returns true for the strings “AGPQrxab” and “xxxxozzzz”, and false for the strings “mortgage” and “discount prescriptions”.

Programming Guidelines

The correctness of your program must not depend on undefined program behavior. Your program must never access out of range positions in a string.

You must use your best programming style, including commenting where appropriate. Be sure that your program builds successfully, and try to ensure that your functions do something reasonable for at least a few test cases. That way, you can get some partial credit for a solution that does not meet the entire specification. To test your program effectively, you should unit test each of your functions individually, and system test your entire program to ensure that all of the functions work together as expected.

One way to organize your program so that you can easily switch between testing individual functions and running the whole program normally is to do something like this:

        const bool unitTesting = true;

        int main()
        {
            if (unitTesting)
            {
                doUnitsTests();
                return 0;
            }
            …  // code for the normal behavior goes here
        }

The doUnitTests function does all your unit tests. To test the whole program normally, just change the value of the unitTesting variable from true to false (and make sure it’s false when you turn in the program).

There are a number of ways you might write doUnitTests. One way is to interactively accept test strings:

        void doUnitTests()
        {
            string s;
            for (;;)
            {
                cerr << "Enter text: ";
                getline(cin, s);
                if (s == "quit")
                    break;
                cerr << "isUppercase returns ";
                if (isUppercase(s))
                    cerr << "true" << endl;
                else
                    cerr << "false" << endl;
                cerr << "getFirstWord returns ";
                cerr << getFirstWord(s) << endl;
            }
        }

While this is flexible, you run the risk of not being able to reproduce all your test cases if you make a change to your code and want to test that you didn’t break anything that used to work.

Another way is to hard-code various tests and report which ones the program passes:

        void doUnitTests()
        {
            if (getFirstWord("hello there") == "hello")
                cerr << "Passed test 1: getFirstWord("hello there") == "hello")" << endl;
            if (!isUppercase("WoW"))
                cerr << "Passed test 2: !isUppercase("WoW")" << endl;
            …
        }

This can get rather tedious. Fortunately, the library has a facility to make this easier: assert. If you include the header <cassert> you can call assert in the following manner:

        assert(some boolean expression);

During execution, if the expression is true, nothing happens and execution continues normally; if it is false, a diagnostic message is written telling you the text and location of the failed assertion, and the program is terminated. As an example, here’s a very incomplete set of tests:

        #include <cassert>

        …

        void doUnitTests()
        {
            assert(getFirstWord("hello there") == "hello");
            assert( isUppercase("WOW!!") );
            assert( !isUppercase("WoW!!") );
            string s = "***hello there";
            assert( extractWord(s) == "hello"  &&  s == " there" );
            assert( extractWord(s) == "there"  &&  s == "" );
            assert( extractWord(s) == ""  &&  s == "" );
            …
            cerr << "All tests succeeded" << endl;
        }

The reason for writing one line of output at the end is to ensure that you can distinguish the situation of all tests succeeding from the case where one function you’re testing silently crashes the program.

Expert Answer

 

//main.cpp

#include <iostream>

#include <string>

#include <locale>

#include <cassert>

using namespace std;

const bool UNIT_TESTING = true;

const bool SYSTEM_TESTING = false;

// Function Prototypes

string getFirstWord(string text);

string getLastWord(string text);

string extractWord(string& text);

bool isUppercase(string text);

string makeUppercase(string text);

bool hasMultipleExclamations(string text);

bool isGibberishWord(string text);

bool isVowel(char character);

void doUnitTesting();

void doSystemTesting();

int main() {

// TESTING

if (UNIT_TESTING) doUnitTesting();

if (SYSTEM_TESTING) doSystemTesting();

string subjectLine;

// cout << “Enter the subject line of the email: “;

// cin >> subjectLine;

// cout << “Enter the body of the email. Press Enter on an empty line to finish.” << endl;

}

// Goes through “text”, and returns the first word it finds.

// A word is a contiguous sequence of letters delimited by a non-letter or end of string.

// If text has no words, returns an empty string.

string getFirstWord(string text) {

if (text.size() == 0) // Empty string passed in

return “”;

string firstWord = “”;

for (size_t i = 0; i != text.size(); i++) {

if (isalpha(text[i])) {

while (isalpha(text[i])) { // Found start of word

firstWord += text[i];

i++;

}

return firstWord; // Finished reading word

}

}

if (firstWord.size() == 0) // No words found

return “”;

}

// Goes through “text”, and returns the last word it finds.

// If text has no words, returns an empty string.

string getLastWord(string text) {

if (text.size() == 0) // Empty string passed in

return “”;

string currentWord = “”;

for (size_t i = 0; i != text.size(); i++) {

if (isalpha(text[i])) {

currentWord = “”; // Resets current word incase a word was previously found

while (isalpha(text[i])) { // Found the start of a word

currentWord += text[i];

i++;

}

i–; // Because of the while loop, i is +1 higher than it should be

// Finished reading word

}

}

if (currentWord.size() == 0)

return “”;

return currentWord;

}

string extractWord(string& text) {

if (text.size() == 0) // Empty string passed in

return “”;

string firstWord = “”;

for (size_t i = 0; i != text.size(); i++) {

if (isalpha(text[i])) {

int firstWordStartIndex = i; // Found start of word

while (isalpha(text[i])) {

firstWord += text[i];

i++;

}

// Finished reading word

int modifiedTextStartIndex = i;

text = text.substr(modifiedTextStartIndex); // Remove all text before and including “firstWord” from “text”

return firstWord;

}

}

if (firstWord == “”) { // No words found

text = “”;

return “”;

}

}

bool isUppercase(string text) {

if (text.size() == 0) return true; // Empty String

bool result = true;

for (size_t i = 0; i < text.size(); i++) {

if (isalpha(text[i]) && !isupper(text[i])) // Found lowercase letter

result = false;

}

return result;

}

// Returns a string identical to “text” but with all letters capitalized

string makeUppercase(string text) {

string resultString = “”;

for (size_t i = 0; i < text.size(); i++) {

if (isalpha(text[i]) && islower(text[i])) // Found lowercase letter

resultString += toupper(text[i]);

else

resultString += text[i];

}

return resultString;

}

// Returns true if “text” has 3 or more consecutive ‘!’ characters

bool hasMultipleExclamations(string text) {

if (text.size() == 0) return false; // Empty string passed in

for (size_t i = 0; i < text.size() – 2; i++) {

if ( text[i] == ‘!’ &&

text[i + 1] == ‘!’ &&

text[i + 2] == ‘!’

) return true;

}

return false;

}

// Returns true if “text” has at least 4 consecutive consonants

bool isGibberishWord(string text) {

if (text.size() == 0) return false; // Empty string passed in

for (size_t i = 0; i < text.size() – 3; i++) {

if (isalpha(text[i]) && !isVowel(text[i]) &&

isalpha(text[i + 1]) && !isVowel(text[i + 1]) &&

isalpha(text[i + 2]) && !isVowel(text[i + 2]) &&

isalpha(text[i + 3]) && !isVowel(text[i + 3])

) return true;

}

return false;

}

bool isVowel(char character) {

switch (character) {

case ‘a’:

case ‘e’:

case ‘i’:

case ‘o’:

case ‘u’:

case ‘A’:

case ‘E’:

case ‘I’:

case ‘O’:

case ‘U’:

return true;

default:

return false;

}

}

void doUnitTesting() {

// getFirstWord() Test

assert(getFirstWord(” Hello HHell”) == “Hello”);

assert(getFirstWord(“”) == “”);

assert(getFirstWord(“*&#8347320”) == “”);

assert(getFirstWord(” “) == “”);

assert(getFirstWord(“hi4 hi “) == “hi”);

assert(getFirstWord(“hi”) == “hi”);

// getLastWord() Test

assert(getLastWord(” Hello HHell”) == “HHell”);

assert(getLastWord(“”) == “”);

assert(getLastWord(“*&#8347320”) == “”);

assert(getLastWord(” “) == “”);

assert(getLastWord(“hi4 hi h 3”) == “h”);

// extractWord() Test

string extractWordString1 = ” 231cat cat”;

assert(extractWord(extractWordString1) == “cat”);

assert(extractWordString1 == ” cat”);

string extractWordString2 = “8347320 “;

assert(extractWord(extractWordString2) == “”);

assert(extractWordString2 == “”);

string extractWordString3 = “h 809 h”;

assert(extractWord(extractWordString3) == “h”);

assert(extractWordString3 == ” 809 h”);

// isUppercase() Test

assert(isUppercase(” 3KK 3KK”) == true);

assert(isUppercase(” 3KK 333dK”) == false);

assert(isUppercase(“”) == true);

assert(isUppercase(“2”) == true);

assert(isUppercase(“i”) == false);

assert(isUppercase(“HJHDJd”) == false);

// makeUppercase() Test

assert(makeUppercase(” 3KKK KKK”) == ” 3KKK KKK”);

assert(makeUppercase(” 3KK 333dK”) == ” 3KK 333DK”);

assert(makeUppercase(“”) == “”);

assert(makeUppercase(“HJHDJd”) == “HJHDJD”);

// hasMultipleExclamations() Test

assert(hasMultipleExclamations(“”) == false);

assert(hasMultipleExclamations(“! ! !”) == false);

assert(hasMultipleExclamations(“!! !!3!!!”) == true);

assert(hasMultipleExclamations(“!! !!!3!”) == true);

// isGibberishWord() Test

assert(isGibberishWord(“AGPQrxab”) == true);

assert(isGibberishWord(“xxxxozzzz”) == true);

assert(isGibberishWord(“mortgage”) == false);

assert(isGibberishWord(“discount prescriptions”) == false);

cout << “All unit tests passed” << endl;

return;

}

void doSystemTesting() {

exit(0);

}

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