sub whatchar
{
    my $diff = shift;  # pass a parameter rather than checking a global
    my $char;  # return this value rather than setting a global

    my @zeroto1 = qw/! @ # $ % ^ & * ( )/;  # characters for values <1
        # (the hash mark there will generate a warning, but it's okay)

    if ( $diff <= 0 ) {
        $char = ' ';  # differs from OP code
    }
    elsif ( $diff < 1 ) {
        $char = $zeroto1[int( $diff * 10 )];
    }
    elsif ( $diff < 10 ) {
        $char = ( $diff < 9 ) ? chr( int( $diff ) + ord( '1' )) : '0';
        # are you sure "234567890" is better than "123456789" ??
        # ... $char = chr( int( $diff ) + ord( '0' )) seems okay to me
    }
    elsif ( $diff <= 35 ) {
        $char = chr( int( $diff - 10 ) + ord( 'a' ));
    }
    else {
        $diff = 260 if ( $diff > 260 );
        $char = chr( int( $diff/10 ) - 3 + ord( 'C' ));
    }
    return $char;
}