my $offset = splice @cPosns, rand @cPosns, 1;

##</code><code>##

my $offset = $cPosns[rand @cPosns];

##</code><code>##

while (1) {
   ...
   last;
}

##</code><code>##

...

##</code><code>##

push @cPosns, pos $zazb while $zazb =~ m{(?=c)}g;

##</code><code>##

push @cPosns, $-[0] while $zazb =~ m{c}g;

##</code><code>##

my $pos = -1;
push @cPosns, $pos while ($pos = index($zazb, 'c', $pos+1)) >= 0;

##</code><code>##

sub popnum3 {
    my ( $x, $y, $z ) = @_;  # $_[3] is $zazb
    if ( $y == 0 ) {
        $aob[$x][0] = $initial * ( 1 + $z );
    }
    else {
        my @cPosns;
        push @cPosns, $-[0] while $_[3] =~ m{c}g;
        if (@cPosns) {
            my $offset = $cPosns[rand @cPosns];
            $aob[$x][$y] = $aob[$offset][ $y - 1 ] * ( 1 + $z );
        }
    }
    return $aob[$x][$y];
}