Today we will learn the Fibonacci Series Program in C and also Fibonacci Series in C Program using different loops and user-defined functions. But, before starting you must have knowledge of Fibonacci Series. So, we will learn it first.

What is Fibonacci Series?

The Fibonacci Series is a never-ending Sequence where the next upcoming term is the addition of the previous two terms. The Fibonacci Series starts with 0,1…

Fibonacci Series: 0,1,1,2,3,5,8,13,21 and so on.

In the above example, you will observe that the series is starting with 0,1 and the third number is 1 because of the addition of the first two numbers.

Fibonacci Series Algorithm:

1 Step: Take an integer variable X, Y and Z

2 Step: Set X=0 and Y=0.

3 Step: Display X and Y.

4 Step: Z=X+Y.

5 Step: Display Z.

6 Step: Start X=Y, Y=Z.

7 Step: Repeat from 4-6, for n times.

There are different methods to print Fibonacci Series we will see that methods one by one.

1. Fibonacci Sequence up to Certain Number

In this program, we will ask the user to enter the number up to which the user wants to print the series.

#include <stdio.h>
int main()
{
  int Number, i = 0, Next, First_Value = 0, Second_Value = 1;

  printf("\n Please Enter the Range Number: ");
  scanf("%d",&Number);
  while(i < Number) 
  {
  	if(i <= 1)
  	{
  		Next = i;
	}
	else
	{
		Next = First_Value + Second_Value;
		First_Value = Second_Value;
		Second_Value = Next;
	}
    printf("%d \t", Next);
   	i++;  
  }
  return 0;
}

Output:

fibonacci series program in c

In the above program, we have declared four integer variables Number, i, First_Value, Second_Value.

Explanation:

1st Iteration: the while condition(0<5) returns TRUE so the while statement will start executing.we have used if-else statement and condition if(0<=1) returns TRUE.So, Next=0 and then if statement block will exit. At last, i will increment.

2nd Iteration: the while condition(1<5) returns TRUE so the while statement will start executing.The condition if(1<=1) returns TRUE.So, Next=1 and then if statement block will exit. At last, i will increment to 1.

3rd Iteration: the while condition(2<5) returns TRUE.if(2<=1) returns FALSE so else statement will start executing.Next=First_Value+Second_Value=0+1=1 and the First_Value=Second_Value=1.So, Second_Value=Next=1 and i is incremented by 1.

4th Iteration: the while condition(3<5) returns TRUE.if(3<=1) returns FALSE so else statement will start executing.Next=First_Value+Second_Value=1+1=2 and the First_Value=Second_Value=1.So, Second_Value=Next=2 and i is incremented to 4.

5th Iteration: the while condition(4<5) returns TRUE.if(4<=1) returns FALSE so else statement will start executing.Next=First_Value+Second_Value=1+2=3 and the First_Value=Second_Value=2.So, Second_Value=Next=3 and i is incremented to 5.

6th Iteration: the while condition(5<5) returns FALSE and the program is exited. And the final output is 0 1 1 2 3.

2. Fibonacci Series up to n Times

This program will print Fibonacci terms up to n times.

#include <stdio.h>
int main() {
    int i, n, t1 = 0, t2 = 1, nextTerm;
    printf("Enter the number of terms: ");
    scanf("%d", &n);
    printf("Fibonacci Series: ");
    for (i = 1; i <= n; ++i) {
        printf("%d, ", t1);
        nextTerm = t1 + t2;
        t1 = t2;
        t2 = nextTerm;
    }
    return 0;
}

Output:

fibonacci series in c program

3. Fibonacci Series in C without Recursion

#include<stdio.h>    
int main()    
{    
 int n1=0,n2=1,n3,i,number;    
 printf("Enter the number of elements:");    
 scanf("%d",&number);    
 printf("\n%d %d",n1,n2);//printing 0 and 1    
 for(i=2;i<number;++i)
   //loop starts from 2 because 0 and 1 are already printed    
 {    
  n3=n1+n2;    
  printf(" %d",n3);    
  n1=n2;    
  n2=n3;    
 }  
  return 0;  
 }    

Output:

without using recursion

4. Fibonacci Series program Using Recursion

Recursion means calling the function again and again until the condition becomes false.

 #include<stdio.h>    
void printFibonacci(int n){    
    static int n1=0,n2=1,n3;    
    if(n>0){    
         n3 = n1 + n2;    
         n1 = n2;    
         n2 = n3;    
         printf("%d ",n3);    
         printFibonacci(n-1);    
    }    
}    
int main(){    
    int n;    
    printf("Enter the number of elements: ");    
    scanf("%d",&n);    
    printf("Fibonacci Series: ");    
    printf("%d %d ",0,1);    
    printFibonacci(n-2);//n-2 because 2 numbers are already printed    
  return 0;  
 }    

Output:

fibinacci series using recursion

Time Complexity: T(n)=T(n-1)+T(n-2) i.e exponential.

In the above program, we can observe that the implementation does lots of repetition so this is very bad implementation for nth Fibonacci Series.

5. Using for Loop

In this program, we will use for loop instead of while loop doesn’t be afraid the logic is the same.

#include <stdio.h>
int main()
{
	int Number, Next, i, First_Value = 0, Second_Value = 1;	
	printf("\n Please Enter the Range Number: ");
	scanf("%d",&Number);	
	/* Find & Displaying Fibonacci series */
	for(i = 0; i <= Number; i++) 
	{
		if(i <= 1)
		{
			Next = i;
	    }
		else
		{
			Next = First_Value + Second_Value;
			First_Value = Second_Value;
			Second_Value = Next;
		}
		printf("%d \t", Next);
	}
	return 0;
}

Output:

fibonacci series in c program

6. Using dynamic Programming

we can store the Fibonacci number to avoid repetition.

#include <stdio.h>  
int fib(int n) 
{ 
    /* Declare an array to store Fibonacci numbers. */
    int f[n + 1]; 
    int i; 
  
    /* 0th and 1st number of the series are 0 and 1*/
    f[0] = 0; 
    f[1] = 1; 
  
    for (i = 2; i <= n; i++) { 
        /* Add the previous 2 numbers in the series 
         and store it */
        f[i] = f[i - 1] + f[i - 2]; 
    }   
    return f[n]; 
}  
int main() 
{ 
    int n = 9; 
    printf("%d", fib(n)); 
    getchar(); 
    return 0; 
} 

Output:

dynamic programming

7. Fibonacci Series in C program Using Functions

In this program, we will use a user-defined function Fibonacci_Series to print a Fibonacci Series Up to n number.

#include<stdio.h>
int Fibonacci_Series(int);
int main()
{
   int Number, i = 0, j;
   printf("\n Please Enter Number upto which you want too: ");
   scanf("%d", &Number);
   printf("Fibonacci series\n");
   for ( j = 0 ; j <= Number ; j++ )
   {
      printf("%d\t", Fibonacci_Series(j));
   }
    return 0;
}
int Fibonacci_Series(int Number)
{
   if ( Number == 0 )
      return 0;
   else if ( Number == 1 )
      return 1;
   else
      return ( Fibonacci_Series(Number - 1) + Fibonacci_Series(Number - 2) );
}

Output:

fibonacci series using functions

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