php-int.php

 <?php

// Case 1 Produces:
// int_of_value: 0 is equal to value: dog
$value = 'dog';

$int_of_value = (int) $value;

if ($int_of_value == $value) {
    /*
     * http://php.net/manual/en/language.operators.comparison.php
     * If you compare a number with a string or the comparison involves numerical strings, then each string is
     * converted to a number and the comparison performed numerically.
     */
    // in this case 'dog' would be converted to an integer when comparing
    echo 'int_of_value: ' . $int_of_value . ' is equal to value: ' . $value;
} else {
    echo 'int_of_value: ' . $int_of_value . ' is NOT equal to value: ' . $value;
}

// Case 2 Produces:
// int_of_value: 0 is NOT equal to value: dog
$value = 'dog';

$int_of_value = (int) $value;

if ($int_of_value === $value) {
    echo 'int_of_value: ' . $int_of_value . ' is equal to value: ' . $value;
} else {
    // strict comparison means string and integer are not equal
    echo 'int_of_value: ' . $int_of_value . ' is NOT equal to value: ' . $value;
}

// Case 3 Produces:
// int_of_value: 0 is NOT equal to value: dog
$value = '0';

$int_of_value = (int) $value;

if ($int_of_value === $value) {
    echo 'int_of_value: ' . $int_of_value . ' is equal to value: ' . $value;
} else {
    // strict comparison means string and integer are not equal
    echo 'int_of_value: ' . $int_of_value . ' is NOT equal to value: ' . $value;
}

// Case 4 Produces:
// int_of_value: 0 is equal to value: 0
$value = 0;

$int_of_value = (int) $value;

if ($int_of_value === $value) {
    // two integers with same value - strict comparison succeeds
    echo 'int_of_value: ' . $int_of_value . ' is equal to value: ' . $value;
} else {
    echo 'int_of_value: ' . $int_of_value . ' is NOT equal to value: ' . $value;
}

// Case 5 Produces:
// no
$value = '0';

if (is_integer($value)) {
    echo 'no';
} else {
    // guessing the 'yes' and 'no' are meant to be switched here?
    // is_integer fails because '0' is a string.  to test for more general numeric use "is_numeric"
    // http://www.php.net/manual/en/function.is-int.php
    echo 'yes';
}

// Case 6 Produces:
// yes
$value = 0;

if (is_integer($value)) {
    // once again, guessing 'yes' and 'no' are switched
    // is integer succeeds because 0 is an integer.
    echo 'no';
} else {
    echo 'yes';
}

What ended up working was ctype -- otherwise -- PHP treats the value as a string. Crazy.

Thanks for your helP!