PHP nested loop Bug

Question

i have developed the following code to find out all armstrong numbers between 100 and 1000, but for some reason is not behaving as expected.

for($i=99;$i<1000;$i++){
    $x = str_split($i);
    $arm = 0;
    foreach ($x as $n){
        $arm = $arm + pow($n,3);
        if ($arm == $i){
            echo $i."\n";
        }
     }
 }

The code checks the value of $i against the value of $arm, if it match, it prints $i. Meaning that $i is a armstrong number. the output is the following.

For some reason is printing twice 370, but according to the first loop $i will hold only once the value of 370. So why im i getting twice 370???

Thanks in advance for any help.

Because at 370 you do: 3^3 + 7^3 which already is equal to 370 and you print the number out in your foreach loop. But adding 0^3 to 370 in the next and last iteration still is equal to 370 and you output the number again. — Rizier123
– Rizier123, Commented Jan 25, 2017 at 22:51
Yep. Basically you need to move the if to after the inner loop. — Don't Panic
– Don't Panic, Commented Jan 25, 2017 at 22:52

Rizier123 · Accepted Answer · 2017-01-25 23:01:11Z

2

You get 370 twice because:

3³ + 7³ == 3³ + 7³ + 0³  //27 + 343  == 27 + 343 + 0

Try to put the if statement after the foreach loop when you have added everything together:

for($i = 99; $i < 1000; $i++){

    $x = str_split($i);
    $arm = 0;

    foreach ($x as $n){
        $arm = $arm + pow($n, 3);
    }

    if ($arm == $i){
        echo $i . "\n";
    }

}

edited Jan 25, 2017 at 23:01

Rizier123

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answered Jan 25, 2017 at 22:53

Maarten van Middelaar

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2 Comments

Maarten van Middelaar Over a year ago

Thanks Rizier123 for adding your contributions to my answer.

Rizier123 Over a year ago

You're welcome :) Don't just say to OP to "try something". Always explain why you changed something in OP's code.

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