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Sep 20th, 2007

Fibonacci Sequence

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I've been asked to write a program that computes the nth Fibonacci number where n is a value input by the user. For example, if n = 6, then the result is 8.
This is what I have so far:

def main():
print "This program will compute nth Fibonacci"
print "number where n is a value input by the user."

x = input("Enter the nth Fibonacci number: ")
s = 1

for i in range(x):
s = s + x

s = s + 1

print "The result is:", s

main()

I believe I'm missing a variable and I can't figure how to get the previous number to add to the next number.

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MakingMoney

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Sep 20th, 2007

Re: Fibonacci Sequence

Preliminary tip: encase your code in [ code="Python ] and [/code] tags (no spaces on the first tag) so that it'll look pretty.

This is a classic case of recursion:

fib(n) = fib(n-1) + fib(n-2)

The best way to compute it is therefore recursively:

Python Syntax (Toggle Plain Text)
>>> def fib(n):
    if n <= 0:
        return 0
    elif n == 1:
        return 1
    else:
        return fib(n-1) + fib(n-2)
>>> def fib(n):
    if n <= 0:
        return 0
    elif n == 1:
        return 1
    else:
        return fib(n-1) + fib(n-2)

This isn't terribly efficient, and perhaps you were supposed to do it with a loop?

Jeff

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Sep 20th, 2007

Re: Fibonacci Sequence

Try looking in the code snippet section of Daniweb to get an idea. There is one in there.

jasimp

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Sep 20th, 2007

Re: Fibonacci Sequence

If you want to access or print all the numbers, append them to a list
test_list = [1, 2] ## Fibs can be started with any 2 numbers
test_list.append( test_list[-1]+test_list[-2] )
print test_list

Last edited by woooee; Sep 20th, 2007 at 10:06 pm.

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Sep 20th, 2007

Re: Fibonacci Sequence

For Python code on Daniweb:
Please use the [code=python] and [/code] tag pair to enclose your python code.

vegaseat

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Mar 13th, 2011

Re: Fibonacci Sequence

The cool and simplest program to get fibonacci series is

Python Syntax (Toggle Plain Text)
n=input('enter the value of n')
a=1
b=2
i=0
print '1'
print '2'
for i in range (0,n-2):
    c=a+b
    print c
    a=b
    b=c
n=input('enter the value of n')
a=1
b=2
i=0
print '1'
print '2'
for i in range (0,n-2):
    c=a+b
    print c
    a=b
    b=c

compiled by__ Ranjith127 & Varun100

Last edited by Ezzaral; Mar 13th, 2011 at 2:26 pm. Reason: Added code tags. Please use them to format all code that you post.

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Nov 19th, 2011

py

This is what I would do:

python Syntax (Toggle Plain Text)
# Filename: fib.py
#!usr/bin/pyton
a = int(input('Enter length: '))
x = 0
y = 1
for i in range(a):
    print(x)
    print(y)
    x = x + y
    y = x + y
# Filename: fib.py
#!usr/bin/pyton
a = int(input('Enter length: '))
x = 0
y = 1
for i in range(a):
    print(x)
    print(y)
    x = x + y
    y = x + y

This is in python 3.1.3

Christopher A.

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Nov 19th, 2011

Re: Fibonacci Sequence

This is very old thread, if you have questions or want critique of your code, start your own fresh thread. Also the OP of this thread wanted to produce single value for nth fibonacci number. That can be made for example like this:

Python Syntax (Toggle Plain Text)
def fib(n):
    prev = [0, 1]
    while n>1:
        prev = prev[-1], sum(prev)
        n -= 1
    return prev[n]
def fib(n):
    prev = [0, 1]
    while n>1:
        prev = prev[-1], sum(prev)
        n -= 1
    return prev[n]

pyTony

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This thread is solved

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