Compute Nth Fibonacci Number

“Compute Nth Fibonacci Number” is similar to problem of printing fibonacci series upto Nth Term, the only difference between is that, in this problem we need to compute and print only Nth Term of the Fibonacci Series, while, in other problem we need to print the fibonacci series up to Nth term. 

Here, we are given a number ‘n’, entered by user and Our task is to compute the nth Fibonacci number.

Fibonacci series: 0, 1, 1, 2, 3, 5, 8…

The first two terms of Fibonacci series are fixed and are 0 and 1. All the succeeding numbers of the Fibonacci series are sum of preceding two numbers.

Like, First term = 0, Second Term = 1

Third Term = Second Term(1) + First Term(0) = 1

Fourth Term = Third Term(1) + Second Term(1) = 2

Fifth Term = Fourth Term(2) + Third Term(1) = 3

.

.

.

So on…

Formula to Compute Nth Fibonacci number:
F(n) = F(n-1) + F(n-2)

Example (Compute Nth Fibonacci number):

INPUT:
N = 5
OUTPUT:
3
INPUT:
N = 6
OUPUT:
5

C++ Program to compute nth fibonacci number is as follows:

/* C++ Program to compute nth fibonacci number */
#include<bits/stdc++.h>  
using namespace std;  
int main()  
{  
    //Scan the number  
    int n;  
    cout<<"Enter the number:";  
    cin>>n;  
      
    // Computing the fibonacci  
    int first = 0;  
    int second = 1;  
    int nth;  
    for(int i = 3; i <= n ; i++)  
    {  
        nth = first + second;  
        first = second;  
        second = nth;  
    }  
      
    // Printing the fibonacci number  
    if(n==1)   
    {  
        cout<<"The nth fibonacci number is "<<first;  
    }  
    else if(n==2)  
    {  
        cout<<"The nth fibonacci number is "<<second;  
    }  
    else  
    {  
    cout<<"The nth fibonacci number is "<<nth;  
    }  
}  

OUTPUT:
Enter the number:5
3

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