C (programming language)

C program to print given number is even or odd using for loop

Understanding Even and Odd Numbers

Before diving into the code, let’s establish a clear understanding of even and odd numbers. An even number is any integer that can be divided by 2 with no remainder. In simpler terms, an even number is perfectly divisible by 2. Conversely, an odd number is any integer that leaves a remainder when divided by 2.

For example, 4, 8, 10, and 12 are even numbers, while 3, 5, 7, and 9 are odd numbers.

Checking Evenness with Modulus Operator

In C, the % operator performs the modulus operation. The modulus of two numbers returns the remainder after dividing the first number by the second. Therefore, checking if a number is even boils down to verifying if the remainder of dividing it by 2 is 0.

For example, if we divide 6 by 2, the result is 3 with a remainder of 0. This means 6 is an even number. Conversely, dividing 5 by 2 gives a result of 2 with a remainder of 1. Hence, 5 is an odd number.

Building the For Loop

Now that we understand evenness and the modulus operator, let’s create a for loop to iterate through a range of numbers and determine their evenness. Here’s the basic structure:


for (int i = start; i <= end; ++i) {
  // Check if i is even
  // Print whether i is even or odd

In this structure:

  • i is the loop counter variable, taking values from start to end (inclusive).
  • The ++i at the end increments the counter after each iteration.
  • The inner block checks if i is even and then prints an appropriate message.

Checking for Evenness Inside the Loop

Within the loop, we need to check if the current value of i is even. As discussed earlier, we can use the modulus operator:


if (i % 2 == 0) {
  // i is even
  printf("%d is even\n", i);
} else {
  // i is odd
  printf("%d is odd\n", i);

This code snippet uses an if statement to check if the remainder of dividing i by 2 is 0. If it is, i is even, and the program prints a message confirming this. Otherwise, i is odd, and the appropriate message is printed.

Putting it All Together

Combining the loop structure and the evenness check, we get the complete C program:


#include <stdio.h>

int main() {
  int start, end;

  // Get the range of numbers from the user
  printf("Enter the starting number: ");
  scanf("%d", &start);
  printf("Enter the ending number: ");
  scanf("%d", &end);

  // Loop through the range and check each number
  for (int i = start; i <= end; ++i) {
    if (i % 2 == 0) {
      printf("%d is even\n", i);
    } else {
      printf("%d is odd\n", i);

  return 0;

This program first prompts the user for the starting and ending numbers of the range. Then, it iterates through this range using a for loop. For each number, the program checks its evenness using the modulus operator and prints the corresponding message.


This C program demonstrates how to use a for loop and the modulus operator to check if a number is even or odd. You can expand on this code by:

  • Modifying the code to check only for even or odd numbers instead of printing both.
  • Adding functionality to count the number of even and odd numbers in the given range.
  • Adapting the program to check whether a specific user-inputted number is even or odd.

By understanding the principles behind this program, you can build upon it and develop more complex solutions to analyze and manipulate numbers in C.


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