MONT 105S Homework 8

Due Wednesday, February 18, at the beginning of class.

Palindromes
A Palindrome is a word or phrase that reads the same way forwards as backwards. For example, the following words are palindromes:

• eve
• madam
• tenet

The following phrases are palindromes (if you remove the spaces and punctuation):

• Madam, I'm Adam
• Able was I ere I saw Elba
• A man, a plan, a canal, Panama

In this assignment, you will write a program to determine whether a word or phrase entered by the user is a palindrome. The program will remove spaces and convert all the characters to lower case before testing to see if the word or phrase is a palindrome. (We will assume the phrases will not use any punctuation).

a) Removing spaces and converting to lower case
You will first write the code to remove all the spaces and convert the word or phrase to all lower case. The program should remove the spaces by stepping through the string, one character at a time, and concatenating the characters to a new string if they are not spaces. Thus, the program should:

• Prompt the user to enter a word or phrase and read it in. Store it in a variable.
• Create a new variable and assign it a value of an empty string (given as "").
• Use a while loop to examine each character in the entered string one at a time.
• If the character is not a space, concatenate that character to the new string variable (use + to concatenate).
• When you are done, the new string variable should contain your string without the spaces.
• After the while loop, use the lower( ) function to convert the new string to all lower case. Recall that you must assign the result to a variable. For example, if your string is named myString, you can convert it to lower case by using the statement:

  myString = myString.lower( )

• Use a print statement at the end of this part of your program to verify that the spaces have been removed and the letters are all lower case.

A sample output of this first half of the program should look as follows.

Sample Output:

Please enter a word or phrase: Able was I ere I saw Elba
ablewasiereisawelba

(User input is underlined.)

b) Detecting a palindrome

Here you will add to the program developed in part a, to determine whether the new string, (that now has spaces removed and is all lower case) is a palindrome.

To detect a palindrome, you should use the following strategy.

• Create a variable to use as a signal (this is known as a "flag") and set its value to True.
• Use a while loop to compare the characters at the ends of the new string created in part a) and work in toward the center. In other words:
  • Compare the first character with the last character. (i.e. compare the character at position zero, with the character at the last position of the string). If they are not the same, set your flag to False. If they are the same, do nothing.
  • Compare the second character with the second to last character. (i.e. compare the character at position 1 with the character at the last position minus 1) If they are not the same, set your flag to False. If they are the same, do nothing.
  • Compare the third character with the third to last character. (i.e. compare the character at position 2 with the character at the last position minus 2) If they are not the same, set your flag to False. If they are the same, do nothing.
  • Repeat until you have compared all the characters with their counterpart at the other end of the string.
  • You should be able to write a single comparison that makes use of your loop counter to indicate the positions of the two characters you are comparing each time through the loop.
• When you are done with the while loop, if any of the characters did not match their counterpart, the flag variable will have become False. Otherwise, the flag variable would have remained True.
• Using a conditional statement, print "You have entered a palindrome." if the flag is True. Otherwise, print "You have not entered a palindrome."

A sample output of the entire program should look as follows.

Sample output 1:

Please enter a word or phrase: Able was I ere I saw Elba
ablewasiereisawelba
You have entered a palindrome!

Sample output 2:

Please enter a word or phrase: Spring is coming
springiscoming
You have not entered a palindrome.

To Submit Your Finished Project:
1. Hand in a hard copy of the file <username>_palindrome.py. Hand this to your instructor in class on the project's due date.

3. Hand in a printout of 2 sample runs like those shown above. Hand this to your instructor in class on the project's due date.

4. Print your name at the top of the cover page and staple it to the top of your hard copy.

5. In addition to the hard copy listed above, email your <username>_palindrome.py file to me at croyden@mathcs.holycross.edu

Get started early and have fun!