What does this mean and how to resolve it ? - 3.55687428096E+14 - php

Question

Ok, so I need this number 3.55687428096E+14 to actually look like a proper whole number. I am not sure what to do in order to make it look like a whole number so that I can go about with my coding. Basically, without resolving this number 3.55687428096E+14, I cant proceed properly. Below is my code, please help!
<?php
$num = 17;
$fact = $num;
echo "The factorial of $num is $num X ";
while ($num > 1){
--$num;
if ($num != 1){
echo "$num X ";
}
else{
echo "$num <b>equals</b> ";
}
$fact = $fact * $num;
}
echo $fact ."<br/>";
?>
By the way, the number 3.55687428096E+14 is the result I am getting after running the program. It comes ok till factorial 16 but once it turns to 17, things become 3.55687428096E+14!

Answer 1

You can user number_format() function if your number is goes very large.
number_format():
The number_format() function formats a number with grouped thousands.
Your code
<?php
$num = 17;
$fact = $num;
echo "The factorial of $num is $num X ";
while ($num > 1){
--$num;
if ($num != 1){
echo "$num X ";
}
else{
echo "$num <b>equals</b> ";
}
$fact = $fact * $num;
}
echo number_format($fact) ."<br/>";
?>

Answer 2

Change the last line with :
echo number_format($fact,0) ."<br/>";

Answer 3

#Mark Baker: - my code below which was executed successfully thanks to your info and support:
<?php
echo "<h2>Find the sum of the digits in the number 100!</h2>"."<br/>";
$num = 100;
$fact = $num;
echo "The factorial of $num is $num X ";
while ($num > 1){
--$num;
if ($num != 1){
echo " $num X ";
}
else{
echo " $num";
}
$fact = bcmul($fact,$num); //right over here!
}
echo " which equals" ."<br/>". "<h3>$fact</h3>";
//proceeding now to calculate the sum of the digits of the factorial!
$_array = str_split($fact);
$sum = array_sum($_array);
echo "The sum of the digits of the factorial is " ."<br/>";
echo "<h3>$sum</h3>";
?>