Write a program which checks a given integer is Fibonacci number or not.

#include<stdio.h>

void main()

{

   int f,s,t,n,i,flg; //’f’ is 1st num,’s’ is 2nd num,’t’ for 3rd new generated num, ‘n’ is user defined, ‘i’ is for iterations, “flg” is Flag variable.

   printf(“Enter a number : “);

   scanf(“%d”,&n); //Read the number.

   if(n<0)

   {

      printf(“Please enter a valid number\n”);

      return;

   }

   f=flg=t=0; //set f,flg and t variables set as zero for check conditions.

   if(n==0)

      flg=1; //set flg variable as ‘1’ for founding the integer in series.

   else

   {

      s=1; //set ‘s’ variable as ‘1’ to generate next numbers of series.

      while(t<n)

      {

         t=f+s; //Generating next number in the series by adding preceding two integers.

         if(n==t)

            flg=1;

         f=s;

         s=t; //Shifting the last two terms of series to ‘f’ & ‘s’ for generating next number in the series.

      }

   }

   if(flg==1)

      printf(“Given integer is a Fibonacci number.\n”);

   else

      printf(“Given integer is Not Fibonacci number.\n”);

   return;

}

Output:

i) Enter a number : 610

Given integer is a Fibonacci number.

ii) Enter a number : 812

Given integer is Not Fibonacci number.

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Task: Write a C program to print nth term in Fibonacci series.