C Program to Check Even or Odd Number

In C, you can check if a number is even or odd by using the modulus operator % like this: if (num % 2 == 0) printf("Even"); else printf("Odd");.

Examples

Input4

Output4 is even

Input7

Output7 is odd

Input0

Output0 is even

How to Think About It

To check if a number is even or odd, divide it by 2 and look at the remainder. If the remainder is 0, the number is even; if it is 1, the number is odd. This uses the modulus operator % which gives the remainder of division.

Algorithm

1

Get input number from the user

2

Calculate remainder when number is divided by 2

3

If remainder is 0, print 'even'

4

Otherwise, print 'odd'

Code

c

#include <stdio.h>

int main() {
    int num;
    printf("Enter an integer: ");
    scanf("%d", &num);
    if (num % 2 == 0)
        printf("%d is even\n", num);
    else
        printf("%d is odd\n", num);
    return 0;
}

Output

Enter an integer: 7
7 is odd

Dry Run

Let's trace the input 7 through the code

1

Input

User enters 7, so num = 7

2

Calculate remainder

7 % 2 = 1

3

Check remainder

Since remainder is 1, condition (num % 2 == 0) is false

4

Print result

Print '7 is odd'

num	num % 2	Condition (num % 2 == 0)	Output
7	1	false	"7 is odd"

Why This Works

Step 1: Using modulus operator

The % operator gives the remainder of division. Even numbers have zero remainder when divided by 2.

Step 2: Condition check

If remainder is zero, the program prints 'even'; otherwise, it prints 'odd'.

Step 3: Input and output

The program reads an integer from the user and outputs the result accordingly.

Alternative Approaches

Using bitwise AND operator

c

#include <stdio.h>

int main() {
    int num;
    printf("Enter an integer: ");
    scanf("%d", &num);
    if ((num & 1) == 0)
        printf("%d is even\n", num);
    else
        printf("%d is odd\n", num);
    return 0;
}

This method uses bitwise AND to check the last bit; it's faster but less intuitive for beginners.

Using ternary operator

c

#include <stdio.h>

int main() {
    int num;
    printf("Enter an integer: ");
    scanf("%d", &num);
    printf("%d is %s\n", num, (num % 2 == 0) ? "even" : "odd");
    return 0;
}

This method uses a compact ternary operator for concise code.

Complexity: O(1) time, O(1) space

Time Complexity

The program performs a single modulus operation and a conditional check, both constant time operations.

Space Complexity

Only a few variables are used, so space is constant.

Which Approach is Fastest?

Bitwise AND is slightly faster than modulus but both are effectively constant time for this task.

Approach	Time	Space	Best For
Modulus operator	O(1)	O(1)	Clarity and simplicity
Bitwise AND operator	O(1)	O(1)	Performance and low-level operations
Ternary operator	O(1)	O(1)	Concise code style