C programs to check if a number is even or odd have been shown here. An integer number $n$ is said to be even if it is divisible by $2$ i.e. $(n\mod 2 = 0)$ and it is called odd if it is not divisible by 2 i.e. it does not result in 0 as the remainder when divided by $2$. So a number in the form of $2n$, where $n$ is an integer, is called even and a number in the form of $2n+1$ or $2n-1$ is called odd. For example $... -4, -2, 0, 2, 4$ ... etc. are even numbers and $... -3, -1, 1, 3, 5$ ... etc. are odd numbers.

Another approach is to apply bitwise AND operator (&) to check if $n$ is even or odd. We need to perform bitwise AND operation between $n$ and $1$. If $n$ AND $1 = 0$, then $n$ is even and if $n$ AND $1 = 1$, then $n$ is odd.

1. Algorithm to check if a number is even or odd

// $n$ is an integer number as input//

1. Check if $n \mod 2 = 0$, then Return Even else

2. Return Odd

2. Pseudocode to check if a number is even or odd

Input: An integer number $n$

Output: If $n$ is even or odd

1. Procedure evenOrOdd($n$):

2. If $n\mod2==0$:

3. Return even

4. Else:

5. Return odd

6. End Procedure

3. Time complexity to check if a number is even or odd

Time Complexity: O(1)

4. C Program to check if a number is even or odd

Code has been copied
/**********************************************
alphabetacoder.com
C program to check if a number is even or odd
***********************************************/

#include <stdio.h>

int main() {
// declare variables
int n;

//take input
printf("Enter the number = ");
scanf("%d", & n);

//check if n is even or odd
if (n % 2 == 0)
printf("%d is even", n);
else
printf("%d is odd", n);

return 0;
}


Output

Case 1:

Enter the number = -5

-5 is odd

Case 2:

Enter the number = 8

8 is even

Case 3:

Enter the number = 3

3 is odd

5. C Program to check if a number is even or odd using bitwise AND operation

Code has been copied
/***************************************
alphabetacoder.com
C program to check if a number is
even or odd using bitwise AND operation
****************************************/

#include <stdio.h>

int main() {
// declare variables
int n;

//take input
printf("Enter the number = ");
scanf("%d", & n);

//check if n is even or odd
// by doing bitwise AND operation
// with 1. If the result is 0 then
// n is even. If the result is 1
// then n is odd.
if (n & 1)
printf("%d is odd", n);
else
printf("%d is even", n);

return 0;
}


Output

Case 1:

Enter the number = 15

15 is odd

Case 2:

Enter the number = 22

22 is even

Case 3:

Enter the number = 13

13 is odd