Math 171 Spring 2005, Lab 10

Due Thursday, March 3, 11:59 P.M.

1. Overview
2. Assignment
3. Hints

Overview

The purpose of this lab is to introduce you to processing character (textual) data in Fortran. You will also gain further practice using loops and branching statements.

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Assignment

Write a Fortran program called paldet that reads in lines from standard input and prints out all the palindromes it finds. Your program should satisfy the following requirements:

• Your program should keep reading standard input until End-Of-File (EOF) is reached. You signal EOF at the keyboard by typing CTRL-D; EOF is generated automatically when redirecting input from a file. You will need to use a READ statement of the form

  
  CHARACTER(len=256) :: charvar
  INTEGER :: status
  
  ...
  
  READ(*,'(A)',IOSTAT=status)  charvar
  
  

  and then test whether the value of status is negative after each READ statement to determine whether EOF has been reached.
• You must handle the case where there are multiple words per line by checking whether each individual word is a palindrome. Note that the READ statement above reads in an entire line, not just one word at once.
• Your program should detect palindromes regardless of how they are capitalized; e.g. Racecar, RAceCAr, and rACECAR should all be detected as palindromes.
• Your program should print out all the palindromes at once, after EOF has been reached on input.
• Your program should be able to handle input lines at least 256 characters long, should be able to process words at least 15 characters long, and should be able to store at least 256 palindromes.

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Hints

1. Since this is the first time you've used the alternate form of the READ statement to detect EOF, start by writing some code that reads in each line of standard input and writes it out again until EOF occurs.
2. Now write some more code to go through each line of input and store each word to a scratch variable using substring specifiers. You will need to find a way to detect the start and end of each word in the line. Print out the values you store in the scratch variable to check that you have this working properly before continuing.
3. Convert each word to all uppercase or lowercase so you won't have to worry about capitalization in the next step. The book has code for converting strings to uppercase; you may want to try converting everything to lowercase to make sure you understand how this code works.
4. Now write some more code using substring specifiers to determine whether the word in your scratch variable reads the same way backward as forward, and make the WRITE statement from step 2 conditional on this criterion.
5. Now create a character variable large enough to hold the required number of palindromes with spaces between them. Instead of writing out the palindromes as you detect them, add them to the end of this character variable. Add a WRITE statement at the end of your program to display this character variable.
6. Finally, test your program some more by hand, and try your program on the Linux online dictionary using the command

   
   ./paldet < /usr/share/dict/words
   
   

   You may also want to try your code on FreeBSD's version of the online dictionary (FreeBSD is another freely available implementation of UNIX). As usual, you will want to compare your results with the output of my code and make sure they are consistent. You may notice that your output automatically gets broken into lines 80 characters in length, which causes some words to be split over multiple lines. However, you don't need to worry about output formatting for this lab.
7. Go back and clean up any extraneous output statements so that only the list of palindromes is printed at the end.

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