Checking if a number is a Fibonacci number through a loop - php

Question

so the task I'm trying to complete here is comparing a user input number against the fibonacci sequence and if it is a fibonacci number the program will echo true, if not it will echo false.
Can someone tell me where I'm going wrong?
this is my first file:
<?php
function print_fibonacci($n){
$first = 0;
$second = 1;
echo "Fibonacci Series: \n";
echo $first.' '.$second.' ';
for($i=2;$i<$n;$i++){
$third = $first + $second;
echo $third.' ';
$first = $second;
$second = $third;
}
}
/* Function call to print Fibonacci series upto 6 numbers. */
print_fibonacci(16);
?>
<form method="POST" action="fibonacci3.php"><br>
<label>Input a number to check if it is fibonacci or not.</label><br>
<input name="fib" type="text" placeholder="#" /><br>
<input type="submit" value="OK!" />
</form>
This outputs the fibonacci sequence until the 16th fibonacci number, and is followed by a form which allows a user to enter a number.
The next file is fibonacci3.php as referenced in the form.
<?php
include "fibonacci2.php";
$n = $_POST["fib"];
function fibonacci($n) {
//0, 1, 1, 2, 3, 5, 8, 13, 21
/*this is an error condition
returning -1 is arbitrary - we could
return anything we want for this
error condition:
*/
if((int)$n <0){
return -1;
echo "False";
}
if ((int)$n == 0){
return 0;
echo "0";
}
if((int)$n == 1 || $n == 2){
return 1;
}
$int1 = 1;
$int2 = 1;
$fib = 0;
for($i=1; $i<=$n-2; $i++ )
{
$fib = $int1 + $int2;
//swap the values out:
$int2 = $int1;
$int1 = $fib;
}
if ($fib = $int1 + $int2 && $n == $fib){
echo "True!";
} else {
echo "False!";
}
return $fib;
}
fibonacci((int)$n);
?>
I thought this might be correct but it's not outputting anything when the user inputs a number.

Answer 1

$n = 'Your number';
$dRes1 = sqrt((5*pow($n, 2))-4);
$nRes1 = (int)$dRes1;
$dDecPoint1 = $dRes1 - $nRes1;
$dRes2 = sqrt((5*pow($n, 2))+4);
$nRes2 = (int)$dRes2;
$dDecPoint2 = $dRes2 - $nRes2;
if( !$dDecPoint1 || !$dDecPoint2 )
{
echo 'True';
}
else {
echo 'False';
}