I was looking though a fellow developers code when I saw this ..
for (;;){
....
....
....
}
I have never seen ";;" used in a loop. What does this do exactly?
It loops forever. ';;' equates to no start value, no stop condition and no increment condition.
It is equivalent to
while (true)
{
...
}
There would usually be a conditional break; statement somewhere in the body of the loop unless it is something like a system idle loop or message pump.
All 3 parts are optional. An empty loop initialization and update is a noop. An empty terminating condition is an implicit true. It's essentially the same as
while (true) {
//...
}
Note that you it doesn't have to be all-or-nothing; you can have some part and not others.
for (init; cond; ) {
//...
}
for (; cond; update) {
//...
}
for (init; ; update) {
//...
}
Just like in C, the for loop has three sections:
a pre-loop section, which executes before the loop starts.
a continuing condition section which, while true, will keep the loop going.
a post-iteration section which is executed after each iteration of the loop body.
For example:
for (i = 1, acc = 0; i <= 10; i++)
acc += i;
will add up the numbers from 1 to 10 inclusive (in C and, assuming you use Perl syntax like $i and braces, in Perl as well).
However, nothing requires that the sections actually contain anything and, if the condition is missing, it's assumed to be true.
So the for(;;) loop basically just means: don't do any loop setup, loop forever (breaks notwithstanding) and don't do any iteration-specific processing. In other words, it's an infinite loop.
Infinite loop. A lot of the time it will be used in a thread to do some work.
boolean exit = false;
for(;;) {
if(exit) {
break;
}
// do some work
}
Infinite Loop (until you break out of it).
It's often used in place of:
while(true) { // Do something }
It's the same as
while(true) {
...
}
It loops forever.
You don't need to specify all of the parts of a for loop. For example the following loop (which contains no body, or update token) will perform a linear search of myArray
for($index = -1; $myArray[++$index] != $target;);
Related
if ( $num_of_things > 1) {
my $max_element = $num_of_things -1;
for($max_element; $max_element >= 0; $max_element--) {
$value_array[$max_element] = $starting_hash{$key}[$max_element];
}
All of my variables not initialized in this code snippet have been initialized as part of the larger subroutine (which I don't want to put up due to length). I'm not sure where I'm getting the useless use of private variable in void context error in this code, my compiler is telling me it's the last line (with nothing but the closing brace "}"). All help is hugely appreciated as I've been staring at this loop for almost an hour with no idea what is wrong.
Move initialization (and declaration) of $max_element into for statement.
[see ooga comment ]
for( my $max_element=$num_of_things-1; $max_element>= 0; $max_element--) {
$value_array[$max_element] = $starting_hash{$key}[$max_element];
}
Is there a way to create something like this in AutoHotKey?
bool isReady = false;
while (!isReady) {
// Do something here
isReady = true;
}
I tried to experiment with While loop, but it ended with just 1 loop regardless of the condition I give the program. I am currently using Version 1.0.47.06.
I read the documentation here: http://www.autohotkey.com/docs/commands/While.htm I tried to give the while loop a value of true. But it only executed once. (I was expecting it to loop forever, until I terminate the script).
condition := true
while (condition)
{
MsgBox, condition
}
while (true)
{
MsgBox, true
}
Your code is correct, but the While command requires version 1.0.48+.
You should update to the latest version of AHK here - http://ahkscript.org/download/
To create a infinite loop , you can use this syntax:
Loop
{
; Your other code goes here
}
I want to create a script that lets me send strings from an array, one by one at the press of a hotkey. (Press once and the first line is sent, press again and the second line is sent and so on) but my (so far limited) comprehension of AutoHotKey fails me.
This is what I have so far (”borrowed” the bit on constructiong the array from the ahk - site)
;Write to the array:
ArrayCount = 0
Loop, Read, C:\My_little_dir\test.txt{ ;test.txt contains 6-digit numbers separated only by ENTER/newline.
ArrayCount += 1 ; Keep track of how many items are in the array.
Arr_Bookings%ArrayCount% := A_LoopReadLine ; Store this line in the next array element.
}
element=1
Change(direction, element, ArrayCount){
if (direction = "next"){
;incrementing from the last element gets us back to the first element
if (element = %ArrayCount%)
{element=1}
else
{element+=1}
}
else{
if (direction = "previous"){
;decrementing from the first element gets us back to the last element
if (element=0)
{element=%ArrayCount%}
else
{element-=1}
}
}
Return Arr_Bookings%element%
}
#N::Send % Change(next,element, ArrayCount)
#B::Send % Change(previous,element, ArrayCount)
However, when I run it, I get an errormessage:
Line Text: #N::Send Change(next,element, ArrayCount)
Error:Hotkeys/hotstrings are not allowed inside functions.
I’ve checked over and over again for messed up curly braces, but to no avail (whitespace carrys no significance...right?).
Any ideas what's causing this?
Also, if you see anything else horribly wrong with this code, feel free to mention it.
Thanks in advance!
/Leo
Autohotkey does not like your indentation style. Use the Allman style.
i.e. put every bracket in its own line and don't use it if you don't have to; for example:
if (element = %ArrayCount%)
{element=1}
else
{element+=1}
braces here are completely superfluous.
I normally wouldn't do this but since i already have the code, here is your unrolled code:
;Write to the array:
ArrayCount = 0
Loop, Read, C:\My_little_dir\test.txt
{ ;test.txt contains 6-digit numbers separated only by ENTER/newline.
ArrayCount += 1 ; Keep track of how many items are in the array.
Arr_Bookings%ArrayCount% := A_LoopReadLine ; Store this line in the next array element.
}
element=1
Change(direction, element, ArrayCount)
{
if (direction = "next")
{
;incrementing from the last element gets us back to the first element
if (element = %ArrayCount%)
{
element=1
}
else
{
element+=1
}
}
else
{
if (direction = "previous")
{
;decrementing from the first element gets us back to the last element
if (element=0)
{
element=%ArrayCount%
}
else
{
element-=1
}
}
}
Return Arr_Bookings%element%
}
#N::Send Change(next,element, ArrayCount)
#B::Send Change(previous,element, ArrayCount)
I've just encountered some very weird behavior that I really can't explain:
do {
my $qry = $self->getHTMLQuery(undef, $mech->content());
next if (!defined($qry));
push(
#prods,
map { 'http://www.XXXXYYYX.com'.$_->attr('href') }
$qry->query('div.prodInfo div.prodInfoBox a.prodLink.GridItemLink')
);
$qry->delete();
$TEST++;
last if ($TEST >= 10);
} while(eval { $mech->follow_link(class => 'jump next') });
print "WHILE ENDED\n";
The code above never prints "WHILE ENDED" even though it does seem to go out of the while loop when $TEST >= 10.
But the following code does print "WHILE ENDED":
do {
my $qry = $self->getHTMLQuery(undef, $mech->content());
next if (!defined($qry));
push(
#prods,
map { 'http://www.XXXXYYYX.com'.$_->attr('href') }
$qry->query('div.prodInfo div.prodInfoBox a.prodLink.GridItemLink')
);
$qry->delete();
$TEST++;
} while(eval { $mech->follow_link(class => 'jump next') } && $TEST <= 10);
print "WHILE ENDED\n";
In both tests, the initial value of $TEST is 0.
Is the behavior of last in do...while different than in for and while {...}?
A do block with a looping modifier doesn't count as a real loop as far as next, last, and redo are concerned. This is mentioned in perlsyn, where you'll find the tip Schwern mentioned about surrounding it with a bare block to make last work. But that won't work with next, because a bare block is only executed once, so next acts like last. To make next work, you can put the bare block inside the do, but then last will act like next.
If you need both next and last to work with a do ... while, the easiest way is to use an infinite loop with the real condition in a continue block. These 2 loops are equivalent, except that the second is a real loop, so it works with next & last:
do { ... } while condition;
while (1) { ... } continue { last unless condition };
From perldoc -f last:
"last" cannot be used to exit a block that returns a value such as
"eval {}", "sub {}" or "do {}"
TLP is right. The standard work around for this (I just hit it myself) is to wrap the do/while in a bare block which, counter-intuitively, does respect loop controls.
{ do {
last;
} while 1; }
The block outside will catch last. If you want to handle next you have to put the bloc inside.
do {{
next;
}} while 1;
The block inside will catch next.
Unfortunately you can't do both.
According to the perl manual for for last (http://perldoc.perl.org/functions/last.html), last can't be used to break out of do {} loops, but it doesn't mention an alternative. The script I'm maintaining has this structure:
do {
...
if (...)
{
...
last;
}
} while (...);
and I'm pretty sure he wants to go to the end of the loop, but its actually exiting the current subroutine, so I need to either change the last or refactor the whole loop if there is a better way that someone can recommend.
Wrap the do "loop" in a bare block (which is a loop):
{
do {
...
if (...)
{
...
last;
}
} while (...);
}
This works for last and redo, but not next; for that place the bare block inside the do block:
do {{
...
if (...)
{
...
next;
}
...
}} while (...);
do BLOCK while (EXPR) is funny in that do is not really a loop structure. So, last, next, and redo are not supposed to be used there. Get rid of the last and adjust the EXPR to evaluate false when that situation is found.
Also, turn on strict, which should give you at least a warning here.
Never a fan of do/while loops in Perl. the do isn't really a loop which is why last won't break out of it. In our old Pascal daze you couldn't exit a loop in the middle because that would be wrong according to the sage Niklaus "One entrance/one exit" Wirth. Therefore, we had to create an exit flag. In Perl it'd look something like this:
my $endFlag = 0;
do {
...
if (...)
{
...
$endFlag = 1;
}
} while ((...) and (not $endFlag));
Now, you can see while Pascal never caught on.
Why not just use a while loop?
while (...) {
...
if (...) {
last;
}
}
You might have to change your logic slightly to accommodate the fact that your test is at the beginning instead of end of your loop, but that should be trivial.
By the way, you actually CAN break out of a Pascal loop if you're using Delphi, and Delphi DID catch on for a little while until Microsoft wised up and came out with the .net languages.
# "http://perldoc.perl.org/functions/last.html":
last cannot be used to exit a block that returns a value such as eval {} , sub {} or do {} , and should not be used to exit a grep() or map() operation.
So, use a boolean in the 'while()' and set it where you have 'last'...
Late to the party - I've been messing with for(;;) recently. In my rudimentary testing, for conditional expressions A and B, what you want to do with:
do {
last if A;
} while(B);
can be accomplished as:
for(;; B || last) {
last if A;
}
A bit ugly, but perhaps not more so than the other workarounds :) . An example:
my $i=1;
for(;; $i<=3 || last) {
print "$i ";
++$i;
}
Outputs 1 2 3. And you can combine the increment if you want:
my $i=1;
for(;; ++$i, $i<=3 || last) {
print "$i ";
}
(using || because it has higher precedence than ,)