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Loop Programs in C

Generate Fibonacci series up to N terms

Introduction

The Fibonacci series is a sequence of numbers in which each number is the sum of the two preceding ones.
It starts with 0 and 1, and continues as:

 C Programs

C Program: Generate Fibonacci series up to N terms

NOTE: The Program is written using for, while and do..while loop.
Method 1 is for loop, Method 2 is while loop and Method 3 is do..while loop

Method 1: Using for loop

C 
#include <stdio.h>


 


int main() {


    int n, i;


    long long first = 0, second = 1, next;


 


    // Input


    printf("Enter the number of terms: ");


    scanf("%d", &n);


 


    // Validate input


    if (n <= 0) {


        printf("Please enter a positive integer.\n");


    } else {


        printf("Fibonacci Series up to %d terms:\n", n);


 


        for (i = 1; i <= n; i++) {


            printf("%lld ", first);


            next = first + second;


            first = second;


            second = next;


        }


        printf("\n");


    }


 


    return 0;


}

Output

 
OUTPUT 1 :
Enter the number of terms: 10
Fibonacci Series up to 10 terms:
0 1 1 2 3 5 8 13 21 34

Explanation

  1. The user enters the number of terms n.
  2. The first two terms are initialized as 0 and 1.
  3. A for loop runs n times:
    • Prints the current term (first)
    • Calculates the next term as next = first + second
    • Updates first and second
  4. The loop continues until all terms are printed.

 

C Program: Generate Fibonacci series up to N terms

Method 2: Using while loop

C 
#include <stdio.h>


 


int main() {


    int n, i = 1;


    long long first = 0, second = 1, next;


 


    // Input number of terms


    printf("Enter the number of terms: ");


    scanf("%d", &n);


 


    // Validate input


    if (n <= 0) {


        printf("Please enter a positive integer.\n");


    } else {


        printf("Fibonacci Series up to %d terms:\n", n);


 


        while (i <= n) {


            printf("%lld ", first);


            next = first + second;


            first = second;


            second = next;


            i++;


        }


        printf("\n");


    }


 


    return 0;


}

Output

 
OUTPUT 1 :
Enter the number of terms: 8
Fibonacci Series up to 8 terms:
0 1 1 2 3 5 8 13

Explanation

  1. The program starts by reading the number of terms n.
  2. It initializes the first two Fibonacci numbers:
    first = 0, second = 1.
  3. The while loop continues until i reaches n.
  4. In each iteration:
    • Print the current term.
    • Compute the next term as next = first + second.
    • Update first and second.
  5. When i > n, the loop stops.

 

C Program: Generate Fibonacci series up to N terms

Method 3: Using do..while loop

C 
#include <stdio.h>


 


int main() {


    int n, i = 1;


    long long first = 0, second = 1, next;


 


    // Input number of terms


    printf("Enter the number of terms: ");


    scanf("%d", &n);


 


    // Validate input


    if (n <= 0) {


        printf("Please enter a positive integer.\n");


    } else {


        printf("Fibonacci Series up to %d terms:\n", n);


 


        do {


            printf("%lld ", first);


            next = first + second;


            first = second;


            second = next;


            i++;


        } while (i <= n);


 


        printf("\n");


    }


 


    return 0;


}

Output

 
OUTPUT 1 :
Enter the number of terms: 10
Fibonacci Series up to 10 terms:
0 1 1 2 3 5 8 13 21 34

Explanation

  1. Initialize:
    • first = 0, second = 1, i = 1.
  2. The do block executes at least once:
    • Prints first.
    • Computes the next Fibonacci number as next = first + second.
    • Updates first and second.
    • Increments i.
  3. The loop continues while i <= n.
  4. The sequence stops after printing N

 

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