Count from 3 in 3 until I reach 10 with php - php

Question

I am trying a basic program to count from 3 in 3 until I reach 10. I tried:
<?php
$a = 0;
$b = 0;
while ($a < 10) {
$a += $b + 3;
echo "$a\n\r";
}
?>
The output is 3, 6, 9, 12. And the expected output would be 3, 6, 9. because I added < 10. Why is it doing this? Sorry for my noob question, but it's confusing: http://codepad.org/Y8yhd0JP

Answer 1

The value of $a is $a=9 in the 3rd iteration, so the loop will continue to go on to add upto 12.
To obtain the result as 3,6,9 check for while($a < 9){...}
<?php
$a = 0;
$b = 0;
while ($a < 9) {
$a += $b + 3;
echo "$a\n\r";
}
?>

Answer 2

This would be better to do with a do-while cycle, with $a initialised to its starting value before the cycle
<?php
$b = 0;
$a += $b + 3;
do {
echo "$a\n\r";
$a += $b + 3;
} while ($a < 10);
?>

Answer 3

The while will check if the value in $a is more than 10.
After the check you add to the value and print it, then check again, if its over 10, it will not do another loop.
So when it prints 12, it will have checked if $a was over 10, which is was not, cause it was 9. Then do the addition and echo and check again and exit.

Answer 4

To start with, note the $b is always 0, so you can eliminate it like this:
$a = 0;
while ($a < 10) {
$a += 3;
echo "$a\n\r";
}
Note that you change the value of $a between the test and the echo. That is probably the reason for your surprise.
A better way to write it would be
for ($a = 3; $a < 10; $a += 3) {
echo "$a\r\n";
}

Answer 5

An uglier solution:
$a = 0;
$b = 0;
while (($a += $b + 3) < 10)
echo "$a\n\r";
I moved the addition in the while loop. Here you dont't have to put the echo in {} because there's only one statement.

Answer 6

in your code you are printing the element after it is increased, so after it prints 9 , it checks the condition ($a < 10) , the condition is true so it proceeds and print 12 , while the next iteration the condition ($a < 10) fails and it stops. this is the reason , you can avoid it by changing your code as follows,
<?php
$a = 0;
$b = 0;
while ($a < 9) {
$a += $b + 3;
echo "$a\n\r";
}
?>
Hope it helps.