CODEWITHSUNDEEP
phpfor-loop
jaons
jaons

Reputation: 7

Php for nested loop

please someone can explain me in detailed way how this loop in php works?

for($a=1;$a<10;$a++) 
{
    echo "<br>";

    for ($b=0;$b<$a;$b++)
    echo $a;

}

Why the output is 1 22 333 4444 55555 etc and not just 1 2 3 4 5 and so on, i know is something elementary but i cannot get it.

thank you.

Upvotes: 1

Views: 8776

Answers (3)

Rho
Rho

Reputation: 1010

There are two loops in your code, the outer loop initialize the value of $a as 1

$a = 1;

Then in the inner loop $b is set to 0 

$b = 0;

The condition for the inner loop to succeed in its first execution is 

$b < $a

Or if you don't follow it, 

0 < 1

Because remember the inner loop initialize $b as 0, and $a is initialized in the outer loop as 1

So 0 is less that 1, so it will succeed and execute 

echo $a; // 1

The inner loop will only execute it 1 time because in its second iteration $b is already 1

$b++

Now it will go to the outer loop again, and $a will equal to 2 because the for loop just did 

$a++

2 is less than 10 so it will execute the second loop again. But now the second loop is condition changes because

$b < $a // 0 < 2

Because remember $a is now equal to 2! So the condition succeed and it will execute

echo $a // or 2

Then after executing in its first try, the for loop will do $b++ so $b will become 1.

SO now, the for loop will test the condition again and the result will be

$b < $a // 1 < 2

1 is less than 2 so it will execute the echo statement again

echo $a // 2

Hence you get 22

Then after that the for loop will do $b++, so now $b is 2 already! Because 2 is not less than 2, hence it will fail and go to the outer loop again.

Upvotes: 2

marramgrass
marramgrass

Reputation: 1411

Each time through the outer loop, the inner loop is performed a times. So 1 is echoed once, 2 is echoed twice, and so on.

Upvotes: 1

Pekka
Pekka

Reputation: 449395

The key is the $a in the inner loop. 

for ($b=0;$b<$a;$b++) 
             ^-------------- HERE

this will count from zero to $a (which is increased every time) in every loop and output $a as many times.

 $a = 0:  no output (inner loop runs from 0 to 0)
 $a = 1:  1 output  (inner loop runs from 0 to 1)
 $a = 2:  2 outputs (inner loop runs from 0 to 2)
 $a = 3:  3 output  (inner loop runs from 0 to 3)
 etc.....

Upvotes: 6

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