Perl II Problem Set:

1.        Create a script that takes two numbers from the command line and
adds them.
                   % add.pl 2 3

                   5

2.        Modify the "add" script from the previous problem set so that it checks that both arguments are defined (hint, use function defined.)

                   % add.pl 2 3

                   5

                   % add.pl 2

                   Please provide two numbers.    

3.        Modify the script again so that it checks that both arguments are positive numbers. Zero is allowed, but -1 is not:

                      % add.pl 2 -3

                      Please provide two positive numbers.    

 

 

4.   Write a script to compare two strings given on the command line arguments and print "right order" if they are in alphabetic order, and "wrong order" if they are not:

                      % order.pl Fred Lucy

                      right order

                      % order.pl Lucy Fred

                      wrong order

                 

5.  Write a script to compare two strings given on the command line and print them out in correct alphabetic order:

                  % reorder Fred Lucy

                  Fred Lucy

                  % reorder Lucy Fred

                  Fred Lucy

                 

6.        Write a script named "same.pl" to read two strings from the terminal. Compare them in a case-sensitive manner and print "same" if they are the same, "different" if they are different:

                  % same.pl

                  Enter string 1: lucy

                  Enter string 2: Lucy

                  different

                 

7.        Modify this script to compare the strings in a case-INsensitive manner (hint, use the "lc" or "uc" functions to change string to upper or lowercase.

8.  Write a script named "percent.pl" to calculate percentages, where the percentage is $i/($i+$j) * 100. Make sure that the script does not crash when given two numbers that add up to zero:

                  % percent.pl 50 150

                  25%

                 

                  % percent.pl 50 -50

                  You are trying to trick me! at line 4.

                 

9.   Modify this script to use the printf() function to produce nicely formatted floating point numbers (hint:  try "man sprintf" and "man printf" or look it up online to learn about this wonderful function).

                  % percent.pl 50 150

                  25.00 %

                 
10.  Write a program named "pali.pl" to detect palindromes. It must be able to handle changes in case.

                  % pali.pl "Madam in Eden Im Adam"

                  yes!

                  % pali.pl gatcctag

                  yes!

                  % pali.pl "cold spring harbor laboratory"

                  no!

                 

11.        Modify the program to work even if there is extraneous punctuation:

                  % pali.pl "A man, a plan, a canal... Panama"

                  yes!

                 

        (Hint: Look up the s/// pattern matching & substitution function in the Perl reference guide. We will cover this formally in a few days, so you can save this one for later if you like.)


12.  Create a file of numbers call numbers.txt with the following content:

22
45
1
2
31
32
72
24



Extra Credit (Topics to be covered in next lecture):

        Here is pseudo-code for a program which uses numbers.txt as input:

                  create file myresult.txt and open it for writing output

                  open numbers.txt for reading

                  while (each line of the file numbers.txt) {

                    if (the number is even) {

                              if (the number is less than 24) {

                                          print the line to STDOUT

                              }

                    }
                    else {

                              compute the factorial of the number

                              print the factorial to the file myresult.txt (one per line)

                    }

                  }



        a. What will be printed to STDOUT?
        b. What will be the contents of myresult.txt?

        c. Convert the pseudocode above into a real program.