Calculate nth fibonacci Number using C program

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Description : 

This program accepts one integer(n) as input and calculate the nth number in Fibonacci Series. As we discussed earlier Fibonacci series starts with 0 and 1. so 0 is the 0th  Fibonacci number and 1 is 1st Fibonacci Number. like this our program will calculate nth Fibonacci number.

Here is the first 10 Fibonacci numbers list :

  • 0 : 0
  • 1 : 1
  • 2 : 1
  • 3 : 2
  • 4 : 3
  • 5 : 5
  • 6 : 8 
  • 7 : 13
  • 8 : 21 
  • 9 : 34 
  • 10 : 55

Program :

  1. /* C program to calculate nth Fibonacci Number
  2.  * Author : Venkatesh Macha
  3.  */
  4. #include<stdio.h>
  5. void main()
  6. {
  7.         int i,j,k,num,cnt;
  8.         printf(“Enter which fibonacci number you want to print : “);
  9.         scanf(“%d”,&num);
  10.         /* First two numbers in Fibonacci Series is 0 and 1 so
  11.          * so i am assuming i and j as first and Second Numbers in
  12.          * in Fibonacci Series
  13.         */
  14.         i=0;
  15.         j=1;
  16.         k=i+j;
  17.         if(num==0)
  18.         {
  19.                 printf(“1st Number in Fibonacci Series is : %dn,i);
  20.                 return;
  21.         }
  22.         if(num==1)
  23.         {
  24.                 printf(“2nd Number in Fibonacci Series is : %dn,j);
  25.                 return;
  26.         }
  27.         /* cnt is 1 because we already have i and j as first two numbers i.e 0th and 1st numbers */
  28.         cnt=1;
  29.         for(cnt;cnt<num1;cnt++)
  30.         {
  31.                 i=j;
  32.                 j=k;
  33.                 k=i+j;
  34.         }
  35.         printf(“%dth Number in Fibonacci series is : %dn,num,k);
  36.         return;
  37. }

Output :

Note : If you try to calculate above 46th Fibonacci Number, you will get invalid values (invalid valid means negative values or wrong values ) you can overcome this problem by using long long Integer for i,j,k variables. Above program i used Long int so its max size is 2 giga plus. so up to 46th Fibonacci value i got correct values but when i try to calculate 47th one i got Negative Values. actually 47th Fibonacci number is  2971215073.

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Venkatesh Macha

Hi Guys, I am Venkatesh Macha. I am a programmer and an Open Source enthusiast, Presently working as a Software Engineer. Apart from that, I love to explore new technologies and things.

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