Even or odd of an array in PHP

It's simple, in the check it's comparing to the array and not to the array element, as it should. That is, it always fakes because a array as a whole is always different from the value 0. It failed the index brackets to get the element:

$par_ou_impar = array(2,3,4,56,5,42,98,100);

for ($i = 0; $i < count($par_ou_impar); $i++){
    if ($par_ou_impar[$i] % 2 == 0)
        echo "O Número é par: $par_ou_impar[$i]<br />";
    else
        echo "O Número é impar: $par_ou_impar[$i]<br />";
}

See running on ideone .

Since you are learning, I suggest you use a control that will prevent the error committed:

$par_ou_impar = array(2, 3, 4, 56, 5, 42, 98, 100);

foreach ($par_ou_impar as $item) {
    if ($item % 2 == 0)
        echo "O Número é par: $item<br />";
    else
        echo "O Número é impar: $item<br />";
}

See working on ideone .

foreach scans the entire array . This is almost always what you want. It better controls this for you. It is always recommended to use it when possible.

You can simplify it even more:

$par_ou_impar = array(2, 3, 4, 56, 5, 42, 98, 100);
foreach ($par_ou_impar as $item) {
    echo "O Número é " . ($item % 2 == 0 ? "par: " : "impar: ") . $item . "<br>";
}

See running on ideone .

In some circumstances you can use the each() function.

Missed you a detail, use [$i] here:

if ($par_ou_impar % 2 == 0)
                ^

to be compared to the element being iterated. So the right code will be:

$par_ou_impar = array(2,3,4,56,5,42,98,100);

for ($i = 0; $i < count($par_ou_impar); $i++){
    if ($par_ou_impar[$i] % 2 == 0)
        echo "O Número é par: $par_ou_impar[$i]<br />";
    else
        echo "O Número é impar: $par_ou_impar[$i]<br />";
}

example: link

I leave my contribution with array_map

function checarNumeros($numeros){
   return ($numeros % 2 ) ? TRUE : FALSE;
}


$parOuImpar  = array(2,3,4,56,5,42,98,100);


$array  = array_map("checarNumeros", $parOuImpar);

print_r($array);

An array is returned, whereas the odd returns 1 and the pairs return 0.

I know it has already been solved, but I leave here an alternative:

<?php
   $par_ou_impar = array(2,3,4,56,5,42,98,100);
   for ($i = 0; $i < count($par_ou_impar); $i++){
       echo ($par_ou_impar[$i] % 2) ? "{$par_ou_impar[$i]} é impar\n" : "{$par_ou_impar[$i]} é par\n";
   }
?>