CSC 4630 Perl 2 adapted from R. E. Beck

I/O and Arithmetic Form pairs of programmer/investigator/discover Exercise 1. Write a program that prompts the user for a number, representing the radius of a sphere. The program prints out the volume of the sphere. (Note: B to 10 significant figures is )

Operator x Exercise 2. Write a program that prompts the user for a (short) string and a positive integer and outputs the string repeated the number of times indicated. For example, with input ha 4 the program gives hahahaha Exercise 3. Modify the previous program to print the output on separate lines, one for each instance of the input string.

Arrays in PERL Look much like lists from LISP except elements must be scalars. Size does not need to be specified initially. Use length as a descriptive measure. Values can be specified by list literals.

List Literals Several forms: –Values separated by commas enclosed in parentheses. (3.4, 5.6, 8.1, 0) (“fred”, “george”, 1, 3) –Values can be determined by expressions, which are evaluated when the literal is used. ($a, $b, $a+$b, $a-$b)

List Literals (2) –The empty list, denoted by () –Values generated by the list constructor operator denoted by.. (1.. 5) generates the list (1, 2, 3, 4, 5) ( ) generates the list (2.2, 3.2, 4.2, 5.2) (0.. 4, 8, 9) generates the list (0, 1, 2, 3, 4, 8, 9) –Values generated by the quote word function qw(alice bob chuck) generates the list (“alice”, “bob”, “chuck”)

Array Variable Holds a single list value, meaning zero or more scalar values. Name starts (rather than $). Can be treated as a whole by certain array operators and array functions. (Similar to LISP or APL)

Array Operators Assignment = # Appends 8 as the first element = qw(one two) = (4, 8, 9) # have the value (4, 5, “one”, “two”, 8, 9) –($a, $b, $c) = (1, 2, 3) # Simultaneous scalar assignment –($a, $b) = ($b, $a) # Swap values (temporary location is hidden)

Array Operators (2) Fancier assignment statements –Embedded array = ($a, $b, $c) $d becomes the value of becomes ($b, $c) –Array sharing, array decomposition $e becomes the first becomes

Array Operators (3) –Length mismatches Too many on right: excess discarded Too many on left: excess set to undef –Length function: implicit $a # sets $a to –Compare with = ($a)

Array Element Access Index origin is 0 = (1..5) $fred[2] is 3 Slice: a subarray chosen by an index list = is (3,4,5)

Array Element List (2) More slices makes the first three elements equal to $fred[1] = (7,8,9) = (2,1,0) = is (9,8,7)

Array Element List (3) $#fred is the index value of the last element So, $fred[$#fred] is the value of the last element And so is $fred[-1] since negative indices count backwards from the end, starting at -1.

Arrays as Stacks push “new”) is equivalent = “new”) $a = removes the last value and assigns it to $a. Right is no better than left unshift “new”) is equivalent =

Arrays as Stacks (2) $a = assigns the first element to $a and removes it

More Array Functions reverse sort chomp