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fibonocci sequence question

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fibonocci sequence question

 
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  #1
Jan 3rd, 2009
What is the first term in the Fibonacci sequence to contain 1000 digits?

so i made a program that finds the fibonocci's sequence (fs).
I tried to do it recursively but it takes too long for big numbers. so i made a manual one.

BUt as i count how many digits there are for each (fs). a problem exist. After F(1476)--which has 309 digits, the program stops suddenly. I think its because of memory space or something. Any ways, this is why I turned to you. any help

here is my code
C++ Syntax (Toggle Plain Text) 
  1. #include<iostream>
  2. #include<fstream>
  3. #include<iomanip>
  4. #include<cmath>
  5. using namespace std;
  6.  
  7. int countdigits(unsigned long double x)
  8. {	
  9. 	int count(0);
  10.  
  11. 	while(x>.99999999999999)
  12. 	{
  13.  
  14. 		x/=10;
  15. 		count++;
  16. 	}
  17. 	return count;
  18. }
  19.  
  20.  
  21.  
  22. int main(){
  23.  
  24. unsigned long double result = 0.0;
  25. unsigned long double x = 1.0;
  26. unsigned long double y = 1.0;
  27. unsigned long double result2 = 0.0;
  28. int count(0);
  29. for(int i = 3;;i++)
  30. {
  31. 	result = x+y;
  32. 	y = x;
  33. 	x = result;
  34. 	result2 = result;
  35. 	cout<<setprecision(10)<<"F of "<<i<<" is : "<<result/1000000<<"	count is : "<<countdigits(result2)<<endl;
  36.  
  37. 	if(( countdigits(result2) == 1000 ) )
  38. 	{
  39.  
  40. 		cin.get();
  41. 	}
  42.  
  43.  
  44. }
  45.  
  46. return 0;
  47. }

try running the program to get a better understanding , and then maybe you can help be better. thanks
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Re: fibonocci sequence question

 
0
  #2
Jan 3rd, 2009
Double's range is higher than int's range, but it's still way less than 1000 digits, at least on my machine.

http://www.cplusplus.com/reference/s...ic_limits.html

It's doubtful you're going to be able to do this problem with the normal data types.
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Re: fibonocci sequence question

 
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  #3
Jan 3rd, 2009
C++ Syntax (Toggle Plain Text) 
  1. unsigned long double result = 0.0;
  2. unsigned long double x = 1.0;
  3. unsigned long double y = 1.0;
  4. unsigned long double result2 = 0.0;
There is no such thing as an unsigned double.

As you only need to use integers, you should try using a 64-bit integer variable type instead of a double, as using a double will also give you inaccurate results. But you wont be able to get accurate big numbers using just the standard C++ library, you will need to use a seperate big number library or class such as this.

Hope this helps.
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Re: fibonocci sequence question

 
0
  #4
Jan 3rd, 2009
If
n! is n * fac(n-1);

Then
log(n!) = n + lfac(n-1)

If you use log10, it's even better
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Re: fibonocci sequence question

 
-1
  #5
Jan 7th, 2009
use a dp solution
#include<iostream.h>
#include<string.h>
#include<vector.h>
#include<iterator.h>
int main()
{
vector<long long int>v1(101);
vector<long long int>v2(101);
int i=0;
for(;i<101;i++)
{
if(i==0||i==1)
v1[i]==1;
else
v1[i]=i;
}
v2[0]=v2[1]=1;
i=2;
for(;i<101;i++)
{
v2[i]=v2[i-1]*v1[i];
}
cout<<"nter no for which u want factorial";
istream_iterator<long long int>is(cin);
ostream_iterator<long long int>os(cout,"\n");
int a;

a=*is;
*os=v2[a];
cout<<"the factorialof "<<a<<"is";
*os;
return 0;
}
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