How work this for loop code (logic)? PHP [closed] - php

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I do not understand the logic of this code. If $ i <5 why not print 5 times * but throw out only one * in first row?
$n = 5;
for ($i = 1; $i <= $n; $i++) {
for ($j = 1; $j <= $i; $j++) {
echo ' * ';
}
echo '<br>';
}
for ($i = $n; $i >= 1; $i--) {
for ($j = 1; $j <= $i; $j++) {
echo ' * ';
}
echo '<br>';
}

Answer 1

The logic is very simple. Look at the first for loop. You have a for loop inside the for loop so as soon as your outer for loop begins, you're inner for loop will also be executed.
For eg,
[FIRST ITERATION] - Your outer for loop starts with $i = 1, so your inner for loop will consider the value of $i as 1 and the inner loop is executed because $j <= $i will be true. So only 1 * is printed.
[SECOND ITERATION] - Your outer for loop starts with $i = 2, so your inner for loop will consider the value of $i as 2 and the inner loop is executed twice because $j <= $i will be true both times as the conditions 1 <= 2 and 2 <= 2 will both return true. So 2 stars(*) are printed.
[THIRD ITERATION] - Your outer for loop starts with $i = 3, so your inner for loop will consider the value of $i as 3 and the inner loop is executed thrice because $j <= $i will be true all the three times as the conditions 1 <= 3, 2 <= 3 and 3 <= 3 will all return true. So 3 stars(*) are printed.
[FOURTH ITERATION] - Your outer for loop starts with $i = 4, so your inner for loop will consider the value of $i as 4 and the inner loop is executed four times because $j <= $i will be true all the four times as the conditions 1 <= 4, 2 <= 4, 3 <= 4 and 4 <= 4 will all return true. So 4 stars(*) are printed.
[FIFTH ITERATION] - Your outer for loop starts with $i = 5, so your inner for loop will consider the value of $i as 5 and the inner loop is executed five times because $j <= $i will be true all the five times as the conditions 1 <= 5, 2 <= 5, 3 <= 5, 4 <= 5 and 5 <= 5 will all return true. So 5 stars(*) are printed.
SECOND OUTER FOR LOOP LOGIC:
[FIRST ITERATION] - Your outer for loop starts with $i = 5, so your inner for loop will consider the value of $i as 5 and the inner loop is executed five times because $j <= $i will be true all the five times as the conditions 1 <= 5, 2 <= 5, 3 <= 5, 4 <= 5 and 5 <= 5 will all return true. So 5 stars(*) are printed.
[SECOND ITERATION] - Your outer for loop starts with $i = 4, so your inner for loop will consider the value of $i as 4 and the inner loop is executed four times because $j <= $i will be true all the four times as the conditions 1 <= 4, 2 <= 4, 3 <= 4 and 4 <= 4 will all return true. So 4 stars(*) are printed.
[THIRD ITERATION] - Your outer for loop starts with $i = 3, so your inner for loop will consider the value of $i as 3 and the inner loop is executed thrice because $j <= $i will be true all the three times as the conditions 1 <= 3, 2 <= 3 and 3 <= 3 will all return true. So 3 stars(*) are printed.
[FOURTH ITERATION] - Your outer for loop starts with $i = 2, so your inner for loop will consider the value of $i as 2 and the inner loop is executed twice because $j <= $i will be true both times as the conditions 1 <= 2 and 2 <= 2 will both return true. So 2 stars(*) are printed.
[FIFTH ITERATION] - Your outer for loop starts with $i = 5, so your inner for loop will consider the value of $i as 5 and the inner loop is executed because $j <= $i will be true. So only 1 * is printed.
Remember that your second outer for loop is not incrementing but it is decremented by one each time you loop is executed. So it starts with 5 and ends with 1.

Answer 2

You start with a main counter $i that runs for each row. It starts at 1 and will stop when it reaches 5 (included) so you will get 5 lines.
Inside that loop you have a star counter $j that starts at 1 and stops when it reaches $i's value (included). So here are the iterations it does :
When $i == 1 :
Iteration 1: $j == 1 : it prints *
$j == $i : the loop stops and prints <br />
When $i == 2 :
Iteration 1: $j == 1 : it prints *
Iteration 2: $j == 2 : it prints *
$j == $i : the loop stops and prints <br />
When $i == 3 :
Iteration 1: $j == 1 : it prints *
Iteration 2: $j == 2 : it prints *
Iteration 3: $j == 3 : it prints *
$j == $i : the loop stops and prints <br />
... And so on until $i == 5 and the loop prints 5 stars before printing <br />
Then you have a second loop where $i starts at 5 and goes down to 1 included (so it will run 5 times) and the inner loop is the same as the first one so it will print as many stars as the value of $i per line. The successive values of $i are 5, 4, 3, 2 then 1 so your script prints 5 stars then 4 then 3 then 2 then 1.
Result :
The code you posted prints the following :
*
* *
* * *
* * * *
* * * * *
* * * * *
* * * *
* * *
* *
*
Just as expected.
If that's not what you expected of your script, please describe the expected behaviour so we can tell you what part should change.