interger problem

[kingdm]

Hi all.

I am trying to solve a problem from project euler, for the purpose of learning I'm not asking here for the answer or logic, I got the latter but it seems that I have a problem in outputting the integer since it exceeds the limit of variable limit in PHP (as I know).

<?php

$a = 0;
$b = 1;
$c = 0;
$even_count = 0;

for( $i = 0 ; $i < 4000000 ; $i++ ) {
    $c = $a + $b;
    $a = $b;
    $b = $c;
    if( $c % 2 == 0 ) {
        $even_count += $c;
    }
}

echo "Sum of all even-valued terms: " . $even_count;

?>

The code is all about the sum of even numbers in the fibbonaci sequence which do not exceed four million.

Whenver I run the program the output as expected is

Sum of all even-valued terms: INF

I can't figure out how to output such big number. Any help? Thanks.

[zimonyi]

What is the result if you call var_dump() on your $even_count variable?

My simple guess is that you have indeed exceeded the limit on your platform for handling numerical values and that if you have a 32BIT operating system you are out of luck. Perhaps with a 64BIT operating system it would be fine.

I checked the PHP manual but I cannot find any object/function that would allow you to store the numerical value as something else and work with it to get around your problem.

Archie

[NogDog]

You could use the BCMath functions, or the PEAR Math_BigInteger package.

[zimonyi]

You could use the BCMath functions, or the PEAR Math_BigInteger package.

Yeah, what NogDog said.

Great that you found them, I knew they should exist but did not know what they might be called. Good to know for future reference.

Archie

[kingdm]

What is the result if you call var_dump() on your $even_count variable?

My simple guess is that you have indeed exceeded the limit on your platform for handling numerical values and that if you have a 32BIT operating system you are out of luck. Perhaps with a 64BIT operating system it would be fine.

Thanks for your reply, I checked the PHP manual but I cannot find any object/function that would allow you to store the numerical value as something else and work with it to get around your problem.

Archie

Whenever I call var_dump() on $even_count variable it outputs float(INF). Yeah you're right, I'm using 32-bit operating system.

You could use the BCMath functions, or the PEAR Math_BigInteger package.

Thanks once more for your reply NogDog, I checked the link you gave me but I can't seem to have an idea how to start using it. Can you give me some samples or simple approach regarding this? Thanks so much.

[zimonyi]

Whenever I call var_dump() on $even_count variable it outputs float(INF). Yeah you're right, I'm using 32-bit operating system.



Thanks once more for your reply NogDog, I checked the link you gave me but I can't seem to have an idea how to start using it. Can you give me some samples or simple approach regarding this? Thanks so much.

As long as you have the package installed (see the Installation section on the link NogDog gave) you just need to exchange your

$even_count += $c;

with

$even_count =  bcadd($even_count, $c);

Archie

[NogDog]

$a = 0;
$b = 1;
$c = 0;
$even_count = 0;
for ($i = 0; $i < 4000000; $i++) {
   $c = bcadd($a, $b);
   $a = $b;
   $b = $c;
   if (bcmod($c, 2) == 0) {
      $even_count = bcadd($even_count, $c);
   }
}
echo "Sum of all even-valued terms: " . $even_count; 

And be prepared to wait awhile, and probably have to use set_time_limit() to allow it to run long enough. (120 seconds was not enough on my PC.)

[kingdm]

Thanks Archie and NogDog for your reply.

Upon reading the BCMath and your replies I finally get the idea how does this things work, however I can't make it run due to some execution time limit.

@NogDog

I wonder where will I set the execution time to greater value, I had looked into the php.ini but the only BCMath related thing I could get is in here

[bcmath]
; Number of decimal digits for all bcmath functions.
; http://php.net/bcmath.scale
bcmath.scale = 0

Sorry for being quite redundant in asking, its just that its not my usual hobby to manipulate the php.ini configurations

[kingdm]

Sorry for my earlier post, after doing some research and trials I found out how to use the set_time_limit(). I added set_time_limit(1000) on top of my php code. But still I got the fatal error for maximum execution time. What is the maximum seconds I could set? Is the problem lies in my 1gb ram laptop?

[zimonyi]

Sorry for my earlier post, after doing some research and trials I found out how to use the set_time_limit(). I added set_time_limit(1000) on top of my php code. But still I got the fatal error for maximum execution time. What is the maximum seconds I could set? Is the problem lies in my 1gb ram laptop?

See set_time_limit() for more details.

Archie

[NogDog]

You can set it to zero (0), which means no time limit. However, before doing that, try setting the maximum for $i in the loop condition to a much smaller number to test your code before letting it loose for 4 million iterations so you can find out if the code is reasonable. If it takes 1/1000th of a second per iteration (purely hypothetically, maybe more, maybe less), you'll need at least 4000 seconds -- a bit over an hour -- for it to run.