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# C++ program to find fibonacci series upto N terms (without and with recursion)

In this chapter of C++ interview questions, we will learn to write:

• c++ program to find fibonacci series
• c++ program to find fibonacci series using recursion

Fibonacci series starts with like this

0,1,1,2,3,5,8,13,21,........

How fibonacci series works?

• Next number we get by adding two numbers before it.
• 0 & 1 are the compulsory in the series.
• 0+1 = 1 → (0,1,1)
• 1+1 = 2 → (0,1,1,2)
• 1+2 = 3 → (0,1,1,2,3) and so on

So we can write equation for fibonacci series as

Fn=Fn-1+Fn-2  with F0=0 and F1=1(here n is a number choosed as input)

Now lets write a program to find fibonacci series in c++.

### C++ program to find fibonacci series using recursion

For recursion there will be a base case  which is n<=1, for any number inputed as n and returns n.

So the mathematical condition is

fibo(n) =n if n<=1

= fibo(n-1)+fibo(n-2) otherwise,

``````#include<iostream>
using namespace std;

int fibo(int n)
{
if(n<=1) // base case
return n;
return fibo(n-1)+fibo(n-2);
}

int main()
{
int n,i=0;
cin>>n;
while(i<n)
{
cout<<" "<<fibo(i);
i++;
}
return 0;
}``````

Output:

4

0 1 1 2

### C++ program to find fibonacci series without recursion

Two pre-defined variable t1,t2 is there and assigned value 0 and 1 respectively.

A for loop will run for the inputed no.(n) of time. In the loop by adding two numbers before, the new number is printed, the series continues.

``````#include <iostream>
using namespace std;

int main() {
int i, n, t1 = 0, t2 = 1, nT;
cin>>n;

for (i = 1; i <= n; ++i) {
cout<<t1<<" ";
nT = t1 + t2;
t1 = t2;
t2 = nT;
}

return 0;
}``````

Output:

5

0 1 1 2 3

cpp interview questions

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