Special Section: Advanced String-Manipulation Exercises

Special Section Advanced String Manipulation Exercises

The preceding exercises are keyed to the text and designed to test your understanding of fundamental string-manipulation concepts. This section includes a collection of intermediate and advanced string-manipulation exercises. You should find these problems challenging, yet entertaining. The problems vary considerably in difficulty. Some require an hour or two of application 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.

29.19

(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 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.

1. Write an application that reads a line 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," and so on.

2. Write an application that reads a line of text and prints a table indicating the number of one-letter words, two-letter words, three-letter words, and so on, appearing in the text. For example, Fig. 29.25 shows the counts for the phrase

   Figure 29.25. Word-length counts for the string "Whether 'tis nobler in the mind to suffer".

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

    

    Whether 'tis nobler in the mind to suffer
   

3. Write an application that reads a line of text and prints a table indicating the number of occurrences of each different word in the text. The first version of your application 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 word "to" three times, the word "be" two times, the word "or" once, and so on. A more interesting (and useful) printout should then be attempted in which the words are sorted alphabetically.

29.20

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

 04/25/1955 and April 25, 1955

 

Write an application that reads a date in the first format and prints it in the second format.

29.21

(Check Protection) Computers are frequently employed in check-writing systems, such as payroll and accounts payable applications. There are many strange stories about weekly paychecks being printed (by mistake) for amounts in excess of $1 million. Incorrect 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 plans to cash a check fraudulently. To prevent a dollar amount from being altered, some 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 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 the 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 an application that inputs a dollar amount to be printed on a check, then prints the amount in check-protected format with leading asterisks if necessary. Assume that nine spaces are available for printing the amount.

29.22

(Writing the Word Equivalent of a Check Amount) Continuing the discussion in Exercise 29.21, 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 written in numbers and spelled out in words as well. Even if someone is able to alter the numerical amount of the check, it is extremely difficult to change the amount in words. Write an application that inputs a numeric check amount and writes the word equivalent of the amount. For example, the amount 112.43 should be written as

ONE hundred TWELVE and 43/100

29.23

(Morse Code) Perhaps the most famous of all coding schemes is the Morse code, developed by SamuelMorse 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 (e.g., period, comma, colon, 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, simply, the absence of a dot or dash. In a sound-oriented system, a space is indicated by a short time during which no sound is transmitted. The international version of the Morse code appears in Fig. 29.26.

Figure 29.26. The letters of the alphabet as expressed in international Morse code.

(This item is displayed on page 1396 in the print version)

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

 

Write an application that reads an English-language phrase and encodes it into Morse code. Also write an application 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.

29.24

(Metric Conversion Application) Write an application that will assist the user with metric conversions. Your application 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 application should recognize invalid conversions. For example, the question

"How many feet are in 5 kilograms?"

 

is not meaningful because "feet" is a unit of length, whereas "kilograms" is a unit of mass.