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Estimate value of e

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Join Date: Sep 2004

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ellas747

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Estimate value of e

Sep 29th, 2004

I'm having problem writing code for a program that estimates the value of the mathematical constant e by using this formula e= 1 + 1/1! + 1/2!...
I just cant get this to work. Can someone please help

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Join Date: Feb 2002

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cscgal

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Re: Estimate value of e

Sep 29th, 2004

Hmm ... start by writing a recurisve function to find the factorial of a number. There's a tutorial on recursion in either the C++ or the Computer Science section of this site - I forget which. You should also be able to find this function by doing a quick google search. Then just add 1/ to your factorial equation and it should do the trick

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ellas747

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Re: Estimate value of e

Sep 29th, 2004

i guess it worked. I'm getting 0 as the answer. who knows.

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ellas747

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Re: Estimate value of e

Sep 30th, 2004

how do you get to calculae a power. is it pow(...)

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Narue

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Re: Estimate value of e

Sep 30th, 2004

>how do you get to calculae a power. is it pow(...)
Yes, that's one way.

I'm here to prove you wrong.

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Join Date: Oct 2004

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ZuK

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Re: Estimate value of e

Oct 2nd, 2004

I know that I'm breaking the rule not to make anybody's homwork.
But since the answer is so simple I can not help it to post a solution

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
#include <iostream>
 
double fakt(int i)
{ 
  if ( i == 1 )
     return 1.0;
  return fakt( i -1 ) * i;
}
 
int main() {
   double e = 1.0;
   for ( int i = 1; i < 4000; i++ ) {
      e += 1.0 / fakt(i);
   }
   std::cout << " e = " << e << std::endl;
   return 0;
}
#include <iostream>

double fakt(int i)
{ 
  if ( i == 1 )
     return 1.0;
  return fakt( i -1 ) * i;
}

int main() {
   double e = 1.0;
   for ( int i = 1; i < 4000; i++ ) {
      e += 1.0 / fakt(i);
   }
   std::cout << " e = " << e << std::endl;
   return 0;
}

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Narue

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Re: Estimate value of e

Oct 2nd, 2004

>for ( int i = 1; i < 4000; i++ ) {
>e += 1.0 / fakt(i);
Wow, I'm impressed if you can fit up to 3999! into a double. I just get undefined behavior when the limit of double is exceeded. :rolleyes:

I'm here to prove you wrong.

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Join Date: Oct 2004

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ZuK

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Re: Estimate value of e

Oct 2nd, 2004

@ Narue: you are right that 170! is the largest nr. that fits into a double.
but with my compiler the result is still correct because fact() simply returns inf for larger numbers then 170 and 1/inf returns 0.0 (btw I'm using gcc )
K.

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Narue

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Re: Estimate value of e

Oct 2nd, 2004

>but with my compiler the result is still correct
That's nice, but your code is still wrong even if the compiler that you use happens to interpret "undefined" as something intelligent.

I'm here to prove you wrong.

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ZuK

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Re: Estimate value of e

#10

Oct 2nd, 2004

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Originally Posted by Narue

>but with my compiler the result is still correct
That's nice, but your code is still wrong even if the compiler that you use happens to interpret "undefined" as something intelligent.

I did not mean to insist on my code being correct. My statement was meant to explain why I did not recognize the mistake in the first place.
K.