C Odd Number Program

What Is an Odd Number?

An integer is odd when it is not divisible by 2. Equivalently, n % 2 is not 0.

n is odd  ⇔  n % 2 != 0

Examples:
  11 % 2 = 1  → odd
   7 % 2 = 1  → odd
  10 % 2 = 0  → even (not odd)
   0 % 2 = 0  → even (not odd)

How to Check an Odd Number in C

Four clear steps — then pick modulo, bitwise, or a step-by-two range loop.

1. Read the integer n (positive, negative, or zero).
2. Compute n % 2 (or check the least significant bit with n & 1).
3. If the remainder is not 0 (or the LSB is 1), n is odd.
4. To list odds in a range, test each value — or start at the first odd and add 2.

Pseudocode

function IsOdd(n):
    return (n mod 2) != 0

function PrintOdds(start, end):
    for i from start to end:
        if IsOdd(i):
            output i

// Faster range listing:
function PrintOddsStep(start, end):
    i = start
    if i is even:
        i = i + 1
    while i <= end:
        output i
        i = i + 2

Cheat Sheet

Keep these facts handy while writing the program.

Live Preview

Enter any integer to see the remainder and the odd/even verdict.

n = 11
n % 2 = 1
(n & 1) = 1
Verdict: ODD

Worked Walkthrough — n = 11

Apply the modulo rule, then confirm with the bitwise check.

Step 1: Compute 11 % 2
        11 = 2 * 5 + 1
        remainder = 1

Step 2: Remainder is not 0 → odd

Step 3: Bitwise check
        11 in binary ends with 1
        (11 & 1) = 1 → same answer

Verdict: 11 is odd

C Programs

Start with the modulo helper — it is the clearest interview answer. Then reuse it for a range, and finish with the bitwise shortcut.

#include <stdio.h>

int is_odd(int n)
{
    return n % 2 != 0;
}

int main(void)
{
    int number = 11;
    if (is_odd(number))
        printf("%d is an odd number.\n", number);
    else
        printf("%d is not an odd number.\n", number);
    return 0;
}

11 is an odd number.

#include <stdio.h>

int is_odd(int n)
{
    return n % 2 != 0;
}

int main(void)
{
    int start = 1;
    int end = 10;
    int i;

    printf("Odd numbers from %d to %d:\n", start, end);
    for (i = start; i <= end; i++)
    {
        if (is_odd(i))
            printf("%d ", i);
    }
    printf("\n");
    return 0;
}

Odd numbers from 1 to 10:
1 3 5 7 9

#include <stdio.h>

int is_odd_bitwise(int n)
{
    return (n & 1) != 0;
}

int main(void)
{
    int samples[] = { 11, 10, 0, -5 };
    int i;

    for (i = 0; i < 4; i++)
    {
        int n = samples[i];
        printf("%d: %s\n", n, is_odd_bitwise(n) ? "odd" : "even");
    }
    return 0;
}

11: odd
10: even
0: even
-5: odd

Time and Space Complexity

A single parity test is constant time. Range printers grow with how many integers you visit.

Key Takeaways