# Perl Programming/Exercise 1 Answers

## A. Getting started, displaying textEdit

#!/usr/bin/perl print "Hello World!\n";

## B. Displaying NumbersEdit

#!/usr/bin/perl # Begin variable definitions $numerator = 4000; # This is the numerator $denomenator = 7; # This is the denominator $answer1 = $numerator / $denomenator; # Answer to part i $dec_places=3;

printf ("%.2f",$answer1);

# End variable definitions print "$numerator divided by $denomenator is: $answer1\n"; $mod_num = $numerator * 10**$dec_places; # Modified Numerator $remainder = $mod_num % $denomenator; $num_div_denom = ($mod_num - $remainder); # $num_div_denom is divisible by denomenator $no_dec_places = $num_div_denom / $denomenator; # This number has no decimal places $answer2 = $no_dec_places / 10**$dec_places; # Answer to part ii print "$numerator divided by $denomenator to 3 decimal places is: $answer2\n"; # Rounds up if the remainder / denominator is > 0.5 $round = $remainder / $denomenator; if ($round > 0.5) { $no_dec_places += 1; } $answer3 = $no_dec_places / 10**$dec_places; # Answer to part iii print "$numerator divided by $denomenator to 3 decimal places, rounded is: $answer3\n"; print "The number with three leading zeros: "; print "0" x 3 . "$answer2\n"; # Answer to part iv if ( $answer1 >= 0 ) { print "The number is positive (+): +$answer\n"; # Answer to part v, first part } else { print "The number is negative (-): $answer\n"; # Answer to part v, second part }

## C. FunctionsEdit

The function:

sub evaluate_delta_and_answer { my($x,$y,$z) = @_; if ($x != 0) { $delta = ($y**2 - (4 * $x * $z)); if ($delta < 0) { print "b^2-4ac is less than zero. Both roots undefined.\n\n"; print "Program Terminated. Goodbye, Dave.\n\n" } elsif ($delta == 0) { $root = (0 - $y) /(2 * $x ); print "b^2-4ac = 0. There will be only one root: " . $root . "\n\n"; print "Goodbye, Dave.\n\n"; } elsif ($delta > 0) { print "b^2-4ac > 0. There will be two roots.\n\n"; $root1 = ((0 - $y) - ($delta)**(0.5)) / (2 * $x); $root2 = ((0 - $y) + ($delta)**(0.5)) / (2 * $x); print "The first root, x1 = " . $root1 . "\n\n"; print "The second root, x2 = " . $root2 . "\n\n"; print "Goodbye, Dave.\n\n"; } } else { print "a = 0. This is not a quadratic function.\n"; print "Goodbye, Dave.\n"; } }

The rest of the program:

print "This program takes three numbers (a, b and c) as coefficients\n"; print "of a quadratic equation, calculates its roots, and displays them\n"; print "on the screen for you.\n\n"; print "Please enter the value of a and press <ENTER>: "; $a = <STDIN>; print "\n"; print "Please enter the value of b and press <ENTER>: "; $b = <STDIN>; print "\n"; print "Please enter the value of c and press <ENTER>: "; $c = <STDIN>; print "\n"; evaluate_delta_and_answer($a,$b,$c);