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. 
To read more visit Wikipedia
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

see also: Fibonacci series in c++ source code with logic explanation