Program describes an easy way to find the Fibonacci numbers below a given number.

Logic:  Fibonacci numbers are the the numbers fall on the Fibonacci series, which grows up accord to Fibonacci rule. The rule is that, the present number in the series is the sum of past number and the number before last. The series starts from 0, and the 2nd term is  1.
Mathematically,

F(n+1) = F(n) + F(n-1)         // F(1) =0 and F(2) = 1

Programmatically, that is what exactly we are doing.  The while loop traces till the upper limit. In each iteration we keep a flag to store last to iteration results to proceed to the next.

To find the fibonacci numbers below a given number.

#include<stdio.h>
void main()
{
int lim_up, A = 0, B = 1, C;
clrscr();
printf(“nnt ENTER THE UPPER LIMIT…: “);
scanf(“%d”, &lim_up);
printf(“nnt FIBONACCI NUMBERS ARE…: “);
while(A<lim_up)
{
printf(“nnttt%d”, A);
C = A + B;
A = B;
B = C;
}
getch();
}
Download exe and source code here.