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C Fibonacci Series

Mathematically, Fibonacci numbers are the sequence of numbers, where every numbers after 0 and 1 are the summation of previous two numbers. For example consider the following series.

0, 1, 1, 2, 3, 5, 8, 13, 21, ... etc

here 5 is the summation of 2 and 3, where as 13 is the summation of 5 and 8 and so on.

Interesting Facts about Fibonacci Series

  • Though Leonardo Pisano Bogollo (1170 - 1250) introduced Fibonacci series, it was used in India hundreds of years before.
  • Fibonacci number sequence are in the format of even number followed by 2 odd numbers i.e) even, odd, odd, even, odd, odd ....
  • Leonardo Pisano Bogollo was the son of Bonacci, thus the name fibonacci were derived.
  • Nov - 23 i.e) 11 - 23 is the only day in fibonacci series.
c fibonacci calender

Pictorical Representation of Fibonacci Series

c fibonacci series

C Program - Fibonacci Series

Let us write a c program to display n fibonacci numbers, here n represents user entered number.

c-fibonacci-series.c
#include <stdio.h>
int main()
{
int a = 0, b = 1, c, i, num;
printf("Enter a number: ");
scanf("%d",&num);
if(num < 1)
{
printf("\nInvalid inuput ");
}
else if(num > 1)
{
printf("\t %d \n\t %d ", a, b);
for(i = 3;i <= num;i++)
{
c = a + b;
a = b;
b = c;
printf("\n\t %d ", c);
}
}
else
printf("%d ", a);
return 0;
}
Enter a number : 5
0 1 1 2 3

Note:

Here, variable a = 0 and b = 1, if user enter number is greater than 1 i.e) 4. for-loop will iterate twice , for the first time c=1, a=1 and b=1 and append the value in c to 0 1 i.e) 0 1 1. Then for the next for-loop iteration c = 2, a = 1, b = 2 and append the value in c to 0 1 1 i.e) 0 1 1 2.

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