# fibonacci series number c++ using while loop example

A program can be coded in different ways and this example shows how to find a number which is in Fibonacci series or not using do while loop
For example 5 is in Fibonacci series where 6 is not
To make it more easy to understand this example shows a dry run in comments at line by line. Hope it will help to understand.
This program covers the concept of while loop and if statement.
Program has tested on code blocks compiler.

C++ source code:

`#include <iostream>using namespace std;int main(){     int n,a,b,next;     cout<<"Enter a number to check if it is a fibonacci number: ";     cin>>n;         // 1)let n=9     if(n==0||n==1)  // 2)check if 9=0 or 9=1 (NOT)     cout<<n<<" is a fibonacci number\n\n";     //skip     else     a=0;b=1;        // 3) a=0 , b=1     next=a+b;       // 4) next=0+1=1     while(next<n)   // 5)loop starts from 1 and continues till next is less then 9     {        a=b;         // 6) a=1      ,9) a=1   ,12)a=2  ,15) a=3   ,18)a=5        b=next;      // 7) b=1      ,10)b=2   ,13)b=3  ,16) b=5   ,19)b=8        next=a+b;    // 8)next=1+1=2   ,11)next=1+2=3   ,14)next=2+3=5   ,17)next=3+5=8                     // 18)next=5+8=13 (loop ends)     }     if(next==n)     // 19)check if 13==9 (NOT)    cout<<n<<" is a fibonacci number";      //skip    else    cout<<n<<" is not a fibonacci number"; // 20)prints that 9 is not a fibonacci number.    return 0;}`

program image:
 c++ Fibonacci number source code
Program input output:
 input = 5