Well, the first reply above was explicitly coded to the OP's questions and the second said it assumed equal length, so they were at least thinking about it but the undef handling is a good point. TIMTOWDI is fun and good practice. How about this? Handles different sized arrays and prints undefs nicely, too.

use strict;
my @a = qw( 1 2 3 );
my @b = qw( 7 8 9 10 );
my ($x, $y) = (1, 2);

for (my $i = 0; $i < @a || $i < @b;  ) {
    printf( "$x: %s $y: %s\n", 
            map { defined $_ ? $_ : 'undef' } ( $a[$i], $b[$i++] ) );
}
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update: side effect -- will extend the shorter array with undefs. Could copy @a and @b before handing to the loop if this was a concern.