C++ Programming Tutorial for Beginners

#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