$start = $a;
$end = ++$a;
for ($_ = $start; $_ <= $end; $_++) { ... }

##</code><code>##

for (++$x .. $x++ . $x) { ... }
# starting at ++$x
# ending at $x++ . $x
# THE END HAS MODIFIED THE START

##</code><code>##

print ++$x, ++$x, ++$x;  # 333

##</code><code>##

$x = 3;
print ++$x/$x--;  # 3/4 => 0.75

##</code><code>##

for (++$x .. $x++ . $x--) { ... }
# or
for (++$....$.++.$.--) { ... }