#!/usr/bin/perl -w

#######################################################
# class2_02_undef
#
# demo how using a value not yet set --- and so containing
# the special Perl value undef --- isn't necessarily an
# error
#
# modified by Sharon Tuttle from "Learning Perl",
#    by Schartz and Phoenix
#
# last modified: 4-10-03
#######################################################

$ct = 1;

# computing (supposedly) the sum and product of the integers 1-10
while ($ct <= 10)
{
    $sum += $ct;   # no error --- initially undef, but treated as zero

    $prod *= $ct;  # OK, not so good --- initially undef, and treated
                   # as 0, but that means it stays 0 (multiplying by 0
		   # and all...!) (note the warning you get, too...)

    $ct++;
}

print("\$ct   is: $ct\n");  
print("\$sum  is: $sum\n");
print("\$prod is: $prod\n");

# end of class2_02_undef