Print First N Odd Numbers in C Using For Loop – Complete Guide

Introduction

In this tutorial, you'll learn how to write a simple C program that prints the first N odd numbers using a for loop. This is a perfect beginner-level problem that helps you understand how loops and number sequences work in C.

What Are Odd Numbers?

Odd numbers are numbers that are not evenly divisible by 2 — they leave a remainder of 1. Examples are: 1, 3, 5, 7, 9, 11... and so on. So, when we say "print the first N odd numbers," we just need to display the first N numbers from this sequence.

How Does the Program Work?

We use a loop that starts from 1 and checks each number one by one. We check if the number is odd using i % 2 != 0. If it is odd, we print it and increase the count. We stop when we've printed N odd numbers.

C Program to Print First N Odd Numbers (Method 1 - Using Modulo Operator)

#include <stdio.h>

int main() {
    int n, i, count = 0;

    printf("Enter the value of N: ");
    scanf("%d", &n);

    printf("First %d Odd Numbers:\n", n);

    for(i = 1; count < n; i++) {
        if(i % 2 != 0)  // If i is odd
        {
            printf("%d ", i);
            count++;
        }
    }

    return 0;
}

Sample Output

Enter the value of N: 5
First 5 Odd Numbers:
1 3 5 7 9

If you enter 10, the output will be:

Enter the value of N: 10
First 10 Odd Numbers:
1 3 5 7 9 11 13 15 17 19

Alternate Method Using Formula (More Efficient)

You can also generate odd numbers using a direct formula: 2 * i - 1. This approach skips the odd/even check and directly gives you odd numbers.

#include <stdio.h>

int main() {
    int n, i;

    printf("Enter the value of N: ");
    scanf("%d", &n);

    printf("First %d Odd Numbers:\n", n);

    for(i = 1; i <= n; i++) {
        printf("%d ", 2 * i - 1);
    }

    return 0;
}

Enter the value of N: 5
First 5 Odd Numbers:
1 3 5 7 9

Program Explanation

This C program asks the user to enter a number N and then prints the first N odd numbers on the screen. It uses a for loop to check each number starting from 1 and prints it only if it's odd. A separate counter keeps track of how many odd numbers have been printed so far. The loop continues until exactly N odd numbers are displayed.

Let's break down the code step by step:

1. Include Header File: #include <stdio.h> includes the standard input/output library.
2. Declare Variables: int n, i, count = 0; declares three variables — n for user input, i as the loop counter, and count to track how many odd numbers have been printed.
3. Get User Input: printf("Enter the value of N: "); prompts the user, and scanf("%d", &n); reads the value.
4. Print Heading: printf("First %d Odd Numbers:\n", n); displays a heading.
5. For Loop: for(i = 1; count < n; i++) runs the loop until count reaches n:
   • Initialization: i = 1 starts the loop counter at 1.
   • Condition: count < n checks if we have printed enough odd numbers.
   • Update: i++ increments the counter after each iteration.
6. Check for Odd Number: if(i % 2 != 0) checks if the current number is odd.
7. Print and Count: printf("%d ", i); prints the odd number, and count++; increments the count.
8. Return: return 0; indicates successful program execution.

Conclusion

This small program is a great way to practice using for loops and conditional logic in C. Understanding how to work with number patterns like odd or even numbers builds a strong foundation for more complex logic ahead. Try extending this code to print even numbers or calculate the sum of odd numbers!

#include <stdio.h>

int main() {
    int n, i, sum = 0;

    printf("Enter the value of N: ");
    scanf("%d", &n);

    for(i = 1; i <= n; i++) {
        sum = sum + (2 * i - 1);
    }

    printf("Sum of first %d odd numbers: %d\n", n, sum);
    return 0;
}

/* Output for N=5: Sum of first 5 odd numbers: 25 */

Frequently Asked Questions

Practice Assignments Using For Loop

Previous Topic: -->> Print Natural Numbers in C   ||   Next topic: -->> Print Even Numbers in C