Fibonacci Series Logic..

[fahadmunir32]

I want some one to explain Fibonacci series logic in c++..
For a Beginner its a difficult to get it completely..
Here is a one method of explain to find Fibonacci series. I Think It Is Well Explanation..

http://fahad-cprogramming.blogspot.com/2013/07/c-program-to-find-fibonaaci-series-with.html

[Manga]

1,2,3,5,8,13,21...

To find the next number in the Fibonacci sequence you would add 21 + 13 and get 34.

There are many ways to create this pattern in C++. You could use a for loop or even recursion.

What exactly do you need?

[manudude03]

I quickly wrote up something which gives you the first number of terms in the Fibonacci series. Maybe not optimum by any means, but it works.

#include <iostream>

using namespace std;

int main()
{
    cout << "How many terms do you want to find?" << endl;
    int Fibonacci;
    cin >> Fibonacci;
    int FibTerms[Fibonacci]; // initializes an array with the number of elements requested.
    if (Fibonacci>=1)
    {
        FibTerms[0]=1;
        cout << FibTerms[0] << " ";
    }
    if (Fibonacci>=2)
    {
        FibTerms[1]=1;
        cout << FibTerms[1] << " ";
    }
    if (Fibonacci>=3)
    {
        for (int i=2; i<Fibonacci; i++) // we have already made the first 2 terms
        {
            FibTerms[i]=FibTerms[i-1]+FibTerms[i-2];//adds the previous 2 terms.
            cout << FibTerms[i] << " ";
        }
    }
    cin.clear();
    cin.ignore(255, '\n');
    cin.get();

}

[Dy7SLyTq]

that doesnt work. you cant have an array with a variable space

[dhruv90]

why can't we have an array with variable space? we can define it's size during runtime.

[Dy7SLyTq]

not in c++ you cant

[manudude03]

I did test the code before I posted it.

http://s293.photobucket.com/user/manudude02/media/fibcpp_zps3024f726.png.html

Only change I made between posting and that screenshot was change the array to type long long so you can have more terms before it hits the number cap.

[Dy7SLyTq]

what compiler are you using?

[manudude03]

GNU GCC compiler

[Dy7SLyTq]

thats weird its not supposed to let you do that

[Manga]

my compiler gives an error when I try that. says value must be constant.

[Dy7SLyTq]

compilers dont usually allow that manga. manudude is the first ive seen to do that. everyone else uses a stl container or dynamic array. dont do what manga did because 99/100 it wont work

[N36fSL3A]

Well if you are using C++ why not.... VECTORS!

cin >> Fibonacci;
std::vector<int> FibTerms;

FibTerms.reserve(Fibonacci);

for(int f = 0; f < Fibonacci; f++)
{
    int temp;
    FibTerms.push_back(temp);
}

That's all you gotta change and it should work.

EDIT - Forgot parenthesis on the pushback function

[Manga]

can you blame me for trying? mandude did it first!

[Dy7SLyTq]

no i dont. im just letting you know for future ref

[N36fSL3A]

So does my example work?

[whitenite1]

And here's using the new command.

// Fibonacci Sequence.cpp : main project file.

#include <iostream>

using namespace std;

int main()
{
    cout << "How many terms do you want to find?" << endl;
    int Fib;
    cin >> Fib;
	const int Fibonacci = Fib;
	int* FibTerms = new int[Fibonacci]; // initializes an array with the number of elements requested.
    if (Fibonacci>=1)
    {
        FibTerms[0]=1;
        cout << FibTerms[0] << " ";
    }
    if (Fibonacci>=2)
    {
        FibTerms[1]=1;
        cout << FibTerms[1] << " ";
    }
    if (Fibonacci>=3)
    {
        for (int i=2; i<Fibonacci; i++) // we have already made the first 2 terms
        {
            FibTerms[i]=FibTerms[i-1]+FibTerms[i-2];//adds the previous 2 terms.
            cout << FibTerms[i] << " ";
        }
    }
    delete [] FibTerms;
    cin.clear();
    cin.ignore(255, '\n');
    cin.get();
}

[N36fSL3A]

You can't set a constant to a variable value in VC++.

That's why you just do this:

cin >> Fibonacci;
std::vector<int> FibTerms;

FibTerms.reserve(Fibonacci);

for(int f = 0; f < Fibonacci; f++)
{
    int temp;
    FibTerms.push_back(temp);
}

//And then continue on with the rest of your program. 

[cire]

There is no reason to use an array or vector at all for this.

The standard requires that array sizes are compile time constants. Compilers that allow VLAs in C++ code do so though an extension that can be disabled so that the compiler is conforming.

Here's an alternate way to approach this:

#include <iostream>

class FibonacciSequence
{
public:
    typedef unsigned long long value_type ;

    FibonacciSequence() : _currentTerm(0), _prevTerm(1) {}
    value_type operator()() ;

private:
    value_type _currentTerm ;
    value_type _prevTerm ;
};

FibonacciSequence::value_type FibonacciSequence::operator()()
{
    value_type term = _currentTerm ;

    _currentTerm += _prevTerm ;
    _prevTerm = term ;

    return term ;
}

int main()
{
    std::cout << "Number of terms to find: " ;
    unsigned nTerms ;
    std::cin >> nTerms ;

    FibonacciSequence seq ;
    for ( unsigned i=0; i<nTerms; ++i )
        std::cout << seq() << ' ' ;

    std::cout << '\n' ;
}

[N36fSL3A]

Well the other guy whipped out code so I was simply fixing it.