Special Section: Advanced String-Manipulation Exercises

Special Section Advanced String Manipulation Exercises

The preceding exercises are keyed to the text and designed to test the reader's understanding of fundamental string-manipulation concepts. This section includes a collection of intermediate and advanced string-manipulation exercises. The reader should find these problems challenging, yet enjoyable. The problems vary considerably in difficulty. Some require an hour or two of program writing and implementation. Others are useful for lab assignments that might require two or three weeks of study and implementation. Some are challenging term projects.

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8.41

(Text Analysis) The availability of computers with string-manipulation capabilities has resulted in some rather interesting approaches to analyzing the writings of great authors. Much attention has been focused on whether William Shakespeare ever lived. Some scholars believe there is substantial evidence indicating that Christopher Marlowe or other authors actually penned the masterpieces attributed to Shakespeare. Researchers have used computers to find similarities in the writings of these two authors. This exercise examines three methods for analyzing texts with a computer. Note that thousands of texts, including Shakespeare, are available online at www.gutenberg.org.

1. Write a program that reads several lines of text from the keyboard and prints a table indicating the number of occurrences of each letter of the alphabet in the text. For example, the phrase

   To be, or not to be: that is the question:
   

   contains one "a," two "b's," no "c's," etc.

2. Write a program that reads several lines of text and prints a table indicating the number of one-letter words, two-letter words, three-letter words, etc., appearing in the text. For example, the phrase

   Whether 'tis nobler in the mind to suffer
   

   contains the following word lengths and occurrences:

   Word length	Occurrences
   1	0
   2	2
   3	1
   4	2 (including 'tis)
   5	0
   6	2
   7	1

    
3. Write a program that reads several lines of text and prints a table indicating the number of occurrences of each different word in the text. The first version of your program should include the words in the table in the same order in which they appear in the text. For example, the lines

   To be, or not to be: that is the question:
   Whether 'tis nobler in the mind to suffer
   

   contain the words "to" three times, the word "be" two times, the word "or" once, etc. A more interesting (and useful) printout should then be attempted in which the words are sorted alphabetically.

8.42

(Word Processing) One important function in word-processing systems is type justificationthe alignment of words to both the left and right margins of a page. This generates a professional-looking document that gives the appearance of being set in type rather than prepared on a typewriter. Type justification can be accomplished on computer systems by inserting blank characters between each of the words in a line so that the rightmost word aligns with the right margin.

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Write a program that reads several lines of text and prints this text in type-justified format. Assume that the text is to be printed on paper 8 1/2 inches wide and that one-inch margins are to be allowed on both the left and right sides. Assume that the computer prints 10 characters to the horizontal inch. Therefore, your program should print 6-1/2 inches of text, or 65 characters per line.

8.43

(Printing Dates in Various Formats) Dates are commonly printed in several different formats in business correspondence. Two of the more common formats are

07/21/1955
July 21, 1955

 

Write a program that reads a date in the first format and prints that date in the second format.

8.44

(Check Protection) Computers are frequently employed in check-writing systems such as payroll and accounts-payable applications. Many strange stories circulate regarding weekly paychecks being printed (by mistake) for amounts in excess of $1 million. Weird amounts are printed by computerized check-writing systems, because of human error or machine failure. Systems designers build controls into their systems to prevent such erroneous checks from being issued.

Another serious problem is the intentional alteration of a check amount by someone who intends to cash a check fraudulently. To prevent a dollar amount from being altered, most computerized check-writing systems employ a technique called check protection.

Checks designed for imprinting by computer contain a fixed number of spaces in which the computer may print an amount. Suppose that a paycheck contains eight blank spaces in which the computer is supposed to print the amount of a weekly paycheck. If the amount is large, then all eight of those spaces will be filled, for example,

1,230.60	(check amount)
--------
12345678	(position numbers)

 

On the other hand, if the amount is less than $1000, then several of the spaces would ordinarily be left blank. For example,

   99.87

--------

12345678

 

contains three blank spaces. If a check is printed with blank spaces, it is easier for someone to alter the amount of the check. To prevent a check from being altered, many check-writing systems insert leading asterisks to protect the amount as follows:

***99.87

--------

12345678

 

Write a program that inputs a dollar amount to be printed on a check and then prints the amount in check-protected format with leading asterisks if necessary. Assume that nine spaces are available for printing an amount.

8.45

(Writing the Word Equivalent of a Check Amount) Continuing the discussion of the previous example, we reiterate the importance of designing check-writing systems to prevent alteration of check amounts. One common security method requires that the check amount be both written in numbers and "spelled out" in words. Even if someone is able to alter the numerical amount of the check, it is extremely difficult to change the amount in words.

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Write a program that inputs a numeric check amount and writes the word equivalent of the amount. Your program should be able to handle check amounts as large as $99.99. For example, the amount 112.43 should be written as

ONE HUNDRED TWELVE and 43/100

8.46

(Morse Code) Perhaps the most famous of all coding schemes is the Morse code, developed by Samuel Morse in 1832 for use with the telegraph system. The Morse code assigns a series of dots and dashes to each letter of the alphabet, each digit and a few special characters (such as period, comma, colon and semicolon). In sound-oriented systems, the dot represents a short sound, and the dash represents a long sound. Other representations of dots and dashes are used with light-oriented systems and signal-flag systems.

Separation between words is indicated by a space, or, quite simply, the absence of a dot or dash. In a sound-oriented system, a space is indicated by a short period of time during which no sound is transmitted. The international version of the Morse code appears in Fig. 8.45.

Figure 8.45. Morse code alphabet.

Character	Code	Character	Code
A	.-	N	-.
B	-...	O	---
C	-.-.	P	.--.
D	-..	Q	--.-
E	.	R	.-.
F	..-.	S	...
G	--.	T	-
H	....	U	..-
I	..	V	...-
J	.---	W	.--
K	-.-	X	-..-
L	.-..	Y	-.--
M	--	Z	--..
Digits
1	.----	6	-....
2	..---	7	--...
3	...--	8	---..
4	....-	9	----.
5	.....	0	-----

 

Write a program that reads an English-language phrase and encodes it into Morse code. Also write a program that reads a phrase in Morse code and converts it into the English-language equivalent. Use one blank between each Morse-coded letter and three blanks between each Morse-coded word.

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8.47

(A Metric Conversion Program) Write a program that will assist the user with metric conversions. Your program should allow the user to specify the names of the units as strings (i.e., centimeters, liters, grams, etc., for the metric system and inches, quarts, pounds, etc., for the English system) and should respond to simple questions such as

"How many inches are in 2 meters?"
"How many liters are in 10 quarts?"

 

Your program should recognize invalid conversions. For example, the question

"How many feet are in 5 kilograms?"

 

is not meaningful, because "feet" are units of length, while "kilograms" are units of weight.