PHP For Loop Confusion - php

Question

Am new to the world of coding and it is my first time understanding loops. I saw an example at a website and am utterly confused by the result.
/* Sample Code 1 */
$counter=0
$start=1
for($start;$start<11;start++) {
$counter=$counter+1;
print $counter;
}
This gives me the result of 1,2,3,4,5,6,7,8,9,10
Now if I update the code as follows
/* Sample Code 2 */
$counter=11;
$start=1;
for($start;$start<11;start++) {
$counter=$counter+1;
print $counter;
}
This gives me the result 12,13,14,15,16,17,18,19,20
However if I update the code as follows
/* Sample Code 3 */
$counter=11;
$start=1;
for($start;$start<11;start++) {
$counter=$counter-1;
print $counter;
}
I get the result 10,9,8.7.6,5,4,3,2,1
Please correct me if I am wrong
If the variable $counter has the value of 11, I am essentially start the increment at 11+1 in the code $counter=$counter+1. Is that correct?
But what confuses me is that how is the result in Sample Code 2 possible if my end value in the FOR loop is $start<11. Doesn't this mean it has to be less than 11?

Answer 1

When you start the loop, $start is less than 11. Then it is incremented at the end of the iteration. Then, the loop ends if it has reached 11.
That is, if $start is 10, then it will enter the loop. It reaches 11, so the for statement exits the loop. It is 11 when the loop ends.

Answer 2

Here is a description i wrote
for (//declare loop
$start = 0; //declare starting value and the value to store it in
$start < 10; // Each time it comes through, if $start is under 10, do the loop. if it is 10, exit
$start++ //Increment $start by 1
)

Answer 3

it seems that you're missing "21" in your second example results.
Could this be the cause of your confusion?

Answer 4

I'll give you an explanation from all example above:
Sample Code 1
$counter=0;
$start=1;
This is variable declaration to declare and initialize both variable.
for($start;$start<11;start++) {
$counter=$counter+1;
for loop has structure:
for({loop initialization}; {loop condition}; {per loop process}){
//the rest of loop process
}
Explanation:
As you can see, example #1 start loop from 1 (taken from $start = 1) and doing loop for as long as $start is smaller than 11. To prevent it from looping forever, that code add $start++ which translate to $start = $start + 1. This way, for every loop, $start is added by 1.
the loop condition has to return true in order the loop to run. If it return false, loop will quit.
Now, let's examine what's inside that loop:
$counter=$counter+1;
print $counter;
You see there: $counter=$counter+1. It means, you increment $counter by one for every loop and print the resulting $counter.
Let's breakdown the process (we start loop # with 1 as it's what's defined by $start = 1):
loop # $start ($start < 11?) $counter ($counter = $counter + 1)
1 1 Y 1
2 2 Y 2
3 3 Y 3
4 4 Y 4
5 5 Y 5
6 6 Y 6
7 7 Y 7
8 8 Y 8
9 9 Y 9
10 10 Y 10
11 11 N 11
From process breakdown above, we can see that condition ($start < 11) is result in false on loop #11. That's why the result is 1..10, not 1..11.
Same goes with Example #2:
$counter=11;
$start=1;
Loop structure:
for($start;$start<11;start++) {
$counter=$counter+1;
Let's breakdown this process:
loop # $start ($start < 11?) $counter ($counter = $counter + 1)
1 1 Y 12
2 2 Y 13
3 3 Y 14
4 4 Y 15
5 5 Y 16
6 6 Y 17
7 7 Y 18
8 8 Y 19
9 9 Y 20
10 10 Y 21
11 11 N 22
This will output 12..21. Because when loop #11 occured, it check that $start < 11 is false. Therefore, loop quit.

Answer 5

Please analyze your code.. you have a clear confusion b/w $start and $ counter variable. please use var_dump so as to see what your variables are going through