I have this code
'$a = "pippo";
$b = "lucia";
for ($i=0;$i<strlen($a);$i++)
{
$c = "$a";
echo "$c";
}'
When I run it I see four times pippo instead of one time. Why does it happen?
Thanks in advance
It echos 'pippo' five times (pippopippopippopippopippo), because your loop says that it should. You start with $i = 0, the loop will continue while that is true. Every time your loop runs $i is incremented by 1. It will stop when the condition $i
Example:
$i = 0
$i = 1
$i = 2
$i = 3
$i = 4
$i = 5 (Will not execute loop, because condition $i<5 is not true anymore)
Related
I am writing one logic to iterate numbers first and then additional logic to putting them into particular subset of array.
What does this code do :
Code accept first $n
its create array of $n number from 1 to $n
Then started converting to subset of $main_array to possible one like
['1'] [1,2] [1,2,3] [2] [2,3] [3] etc. same like this
After creating subset i am counting those some subset which satisfy condition
Condition is xyz[0] should not come in subset with abc[0] vice versa xyz[i] should not come in subset abc[i]. Example 2 and 3 is coming subset then dont count that subset, same 1 and 4 is coming then dont count
here is my nested for loop :
$n = 1299;
$main_array = range(1,$n);
$counter = 0;
$count = sizeof($abc); // $abc and $xyz size will same always.
$abc = [2,1];
$xyz = [3,4];
for ($i=0; $i <$n; $i++) {
for($j = $i;$j < $n; $j++){
$interval_array = array();
for ($k = $i; $k <= $j; $k++){
array_push($interval_array,$main_array[$k]);
}
$counter++;
for ($l=0; $l < $count ; $l++) {
//if block here to additional condition using in_array() php function. which do $counter--
if(in_array($abc[$l], $interval_array) &&
in_array($xyz[$l], $interval_array)){
$counter--;
break;
}
}
}
}
$main_array i have to create on the spot after receiving $n values.
Following is cases :
when running $n = 4 its run in 4s
when running $n = 1200 or 1299 or more than 1000 its run in 60s-123s
Expected execution timing is 9s. I reduce from 124s to 65s by removing function calling inside for loop but its not coming to point.
Expectation of code is if i have array like
$array = [1,2,3];
then
subset need to generate :
[1],[1,2],[1,2,3],[2],[2,3],[3]
Any help in this ?
It's difficult to test performance against your experience, but this solution removes one of the loops.
The way you repeatedly build $interval_array is not needed, what this code does is to just add the new value from the main array on each $j loop. This array is then reset only in the outer loop and so it just keeps the last values and adds 1 extra value each time...
for ($i=0; $i <$n; $i++) {
$interval_array = array();
for($j = $i;$j < $n; $j++){
array_push($interval_array,$main_array[$j]);
// Check output
echo implode(",", $interval_array)."\n";
$counter++;
for ($l=0; $l < $count ; $l++) {
if(in_array($abc[$l], $interval_array) &&
in_array($xyz[$l], $interval_array)){
$counter--;
break 2;
}
}
}
}
adding "\n" to better understanding for subset flow.
import datetime
N = list(range(1, int(input("N:")) + 1))
affected_list = list(map(int, input("affected_list").split()))
poisoned_list = list(map(int, input("poisoned_list").split()))
start_time = datetime.datetime.now()
exclude_list = list(map(list, list(zip(affected_list, poisoned_list))))
final_list = []
for i in range(0, len(N)):
for j in range(i + 1, len(N) + 1):
if N[i:j] not in exclude_list:
final_list.append(N[i:j])
print(final_list)
end_time = datetime.datetime.now()
print("Total Time: ", (end_time - start_time).seconds)
what I am trying to achieve here is to be able to loop from 0 to 100 (100, 98, 96, 94 ...) but has to stop at 0. What is doing right now is it passes 0 and -2 -4 which crashes the server. What am I doing wrong?
for ($i = 100; $i <= 100; $i--){
echo $i--;
echo "<br>";
}
Maybe a little explanation would be useful.
The middle part of the for loop $i <= 100 is what makes it infinite. That expression is checked before each iteration of the loop, and the loop will continue as long as that expression evaluates to true.
Since you set $ito 100 in the first section of the loop, and you're doing nothing except making it smaller, it will always be <= 100, forever.
The loop will work fine just the way you have it written if you change the continuation condition.
for ($i = 100; $i >= 0; $i--){
echo $i--;
echo "<br>";
}
That way it will continue until $i is reduced to less than zero, then $i >= 0 will be false, and the loop will end.
The third argument in for loop is what will be executed at the end of the loop. So:
for ($i = 100; $i >= 0; $i -= 2){
echo "$i<br>";
}
Will do the trick
As you can read here https://secure.php.net/manual/en/control-structures.for.php
At the end of each iteration, expr3 is evaluated (executed).
Alternatively:
<?php
foreach(range(100, 0, -2) as $n) {
echo $n;
}
for ($i = 100; $i >= 0; $i-=1){
echo $i--;
echo "<br>";
}
I figured it out somehow. Has been studying JavaScript for a year; Loop is still confusing to me
I'm somewhat new to PHP, been reading a few books and I've never seen a loop where it gets you all the even numbers(for example from 1 to 10), so I decided to try it myself:
for($i=0;$i<10 && $i % 2===0;$i++)
echo $i;
Tried with only double == as well.
And this,
$i=0;
do echo $i; while($i++<10 && $i % 2 ==0);
Can't seem to figure out how to use 2 conditions in the same statement.
Would appreciate the help!
Thanks.
Try to use this code
for( $i=0; $i<=10; $i++ )
{
if( $i%2 == 0 ){
echo $i;
}
}
The loop is breaking entirely when the second condition fails the first time. On the first iteration: 0 is less than 10, and it is even, so the loop iterates. On the second iteration: 1 is less than 10, but is odd, so the loop breaks.
Your code is the equivalent of this:
for($i=0; $i<10; $i++) {
if ($i % 2 !==0 ) {
break;
}
echo $i;
}
0
You can eliminate the second condition of your for loop to prevent the breakage and rely exclusive on a third expression to increment $i by two each iteration.
for($i=0; $i<10; $i = $i + 2) {
echo $i;
}
02468
The second statement in a for-loop is/are the condition(s) which gets checked every loop. so if it fails your loop stops. what you need will look somewhat like this:
for ($i = 0; $i < 10; $i++)
if ($i % 2 == 0)
echo $i;
So the loop will run over every number but only print out the even ones.
You don't need to loop.
Range can create a range with third parameter step 2.
$arr = range(0,20,2);
Echo implode(" ", $arr);
https://3v4l.org/S3JWV
you can use also regular loop and get the evens by formula:
for($i=0; $i<10 ;$i++) {
$j = $i * 2;
// do somthing with $j witch loop over 10 first evens...
}
I'm a newbie to php and I've understood all other loops in php but the question is I cannot understand how the for loops works for ex:
Here is the code;
$a = 0;
$b = 0;
for ($i=0; $i < 5; $i++) {
$a += 10;
$b += 5;
}
echo("At the end of the loop a=$a and b=$b");
When I execute this script the value of a = 50 and b = 25!
Is it multiplying the a value with i's increment value? like 10 * 5 = 50.
You start with $i=0, then you do $a+10 and $b+5 as long as $i <5
$i=0, $a=10, $b=5
$i=1, $a=20, $b=10
$i=2, $a=30, $b=15
$i=3, $a=40, $b=20
$i=4, $a=50, $b=25
$i=5, now the loop stops because $i is no longer <5
Your loop runs five times. Each time through the loop you add 10 to the value of $a. Doing that five times gives you 50.
This is the way it works.
Let's say you have a no dollars. And I tell you that I will give you a dollar everytime you do 5 chores. However, I will only give you 5 dollars. At first you have no dollars and after one chore I give you 5 dollars. Now you have 5 dollars. You do another chore and I give you another 5, bringing you to ten. I have now given you two dollars. I give you another 5 - you have 15. I give you another - 20 - and one more; bringing you to 25 dollars. Now I have given you my limit of dollars, and our loop is complete.
In this story, my dollars are your $i value. Beginning at 0, working up to 5. Your chores are your $b values, which are added to every time.
Code example:
for ($dollars=0; $dollars < 5; $dollars++) {
$chores += 5;
}
+= is not increment its an assignment operator.
http://php.net/manual/en/language.operators.assignment.php
As I mentioned in the comments, and others in their answers. += will add the value to on the right to the value on the left. so in a loop its like this
step 0 $a = 5 ( 0+5)
step 1 $a = 10 (5[previous iteration exit value]+5 )
step 2 $a = 15 (10[previous iteration exit value] + 5)
so on....
Of note is you can also do -= *= etc. and .=or append all the same kind of operation.
The for statement is used when you know how many times you want to execute a statement or a block of statements.
Syntax:
for (initialization; condition; increment){
code to be executed;
}
The initializer is used to set the start value for the counter of the number of loop iterations. A variable may be declared here for this purpose and it is traditional to name it $i.
Example
The following example makes five iterations and changes the assigned value of two variables on each pass of the loop −
<html>
<body>
<?php
$a = 0;
$b = 0;
for( $i = 0; $i<5; $i++ ) {
$a += 10;
$b += 5;
}
echo ("At the end of the loop a = $a and b = $b" );
?>
</body>
</html>
This will produce the following result −
At the end of the loop a = 50 and b = 25
For loop is entry condition loop. It evaluate condition first, so the statement block associated with the loop won't run even once if the condition fails to meet
The statements inside this for loop block will run 5 times, the value of $i will be 0 to 4;
Imagine the loops are running separately.
$a=0;
$b=0;
for ($i = 0; $i < 5; $i++){
echo $a += 10;
echo '<br>';
}
And the output like this.
10
20
30
40
50
Now another Loop
for ($i=0; $i < 5; $i++) {
echo $b += 5;
echo '<br>';
}
And the output like this
5
10
15
20
25
In each iteration it adds 10 and 5 to previous number of iteration using the assignment operator x += y.
Ive managed to loop through a table and get the difference in days between 2 dates adjacent to each other in the table.
Multiple entries have the same date, i have it now that when that date changes, it displays an image however i want it to display the image as many times as the difference in date
$sql = mysql_query("SELECT * FROM Films_Info")
or die(mysql_error());
$last_value = null;
while ($row = mysql_fetch_assoc($sql)) {
if (!is_null($last_value)) {
$a = new DateTime($row['FilmRelease']);
echo "<p>".$row['FilmName']."</p>";
$interval = $a->diff(new DateTime($last_value));
//echo $interval->format('%d days');
$i = 0;
}
$howManydays = $interval->days;
for ( $i; $howManydays; $i++) {
echo "<img src=\"day.jpg\" />";
$howManydays = 0;
}
$last_value = $row['FilmRelease'];
}
for ( $i = 0; $i < $howManydays; $i++) The second is a conditional statement telling when the loop should stop.
The first section in the for loop where it says $i = 0 initialized the variable $i to 0 and then tests the condition $i < $howManydays.
Let's say $howManydays equals 1. That means 0 < 1, so the loop will perform.
At the end of the loop, the third section is called ($i++), so $i is incremented and now equals 1. The second section is called again to test conditions $i < $howManydays which is asking if 1<1 which it's not, so the loop will exit.
So if $howManydays is greater than 0, the loop should happen the integer amount that is in $howManydays.
You will want to remove $howManydays = 0; within the for loop, if you don't want it to only fire once.
The for loop
for ( $i = 0; $i < $howManydays; $i++){
// ...
}
is somewhat equivalent to the while loop:
$i = 0;
while ( $i < $howManydays ){
// ...
$i++;
}
http://php.net/manual/en/control-structures.for.php for more information
In your code above, you should also check if interval was set. You should probably just do an if rather than a while, if only need one interval.
you could just do a simple division on the interval and print out the image that many times
$last_value_u = $last_value->format('U');
$a_u = $a->format('U');
$interval = $a_u - $last_value_u;
$image_count = intval($interval/86400);
for($i=0;$i<$image_count;$i++)
echo "<p><img src=\"day.jpg\" /></p>";
Update
An alternative option would be to loop through the interval:
for($i=$last_value_u;$i<$a_u;)
{
if(intval(($a_u - $i)/86400) == X)
{
// run special code for specific day
}
else
{
// run code for every other day
}
$i+=86400;
}