Perl II Problem Set:
1. Create a script ("add.pl") that takes two numbers from the command line and adds them.
% add.pl 2 3
5
2. Modify the "add.pl" 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 ("order.pl") 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 ("reorder.pl") to compare two strings given on the command line and print them out in correct alphabetic order:
% reorder.pl Fred Lucy
Fred Lucy
% reorder.pl 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 and 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. |
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