PHP Program to Check Even or Odd Number

Use the modulus operator % in PHP to check if a number is even or odd: if $number % 2 == 0, it is even; otherwise, it is 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 because it divides evenly by 2. If the remainder is 1, the number is odd because it leaves a remainder when divided by 2.

Algorithm

1

Get the input number.

2

Calculate the remainder when the number is divided by 2.

3

If the remainder is 0, print that the number is even.

4

Otherwise, print that the number is odd.

Code

php

<?php
$number = 7;
if ($number % 2 == 0) {
    echo "$number is even";
} else {
    echo "$number is odd";
}
?>

Output

7 is odd

Dry Run

Let's trace the number 7 through the code to check if it is even or odd.

1

Assign number

$number = 7

2

Calculate remainder

7 % 2 = 1

3

Check remainder

Since remainder is 1, number is odd

4

Print result

Output: '7 is odd'

Step	Operation	Value
1	Assign number	7
2	Calculate 7 % 2	1
3	Check if remainder == 0	False
4	Print output	7 is odd

Why This Works

Step 1: Use modulus operator

The % operator gives the remainder of division, which helps determine evenness.

Step 2: Check remainder

If remainder is 0, the number divides evenly by 2 and is even.

Step 3: Print result

Based on the remainder, print whether the number is even or odd.

Alternative Approaches

Using bitwise AND operator

php

<?php
$number = 7;
if (($number & 1) == 0) {
    echo "$number is even";
} else {
    echo "$number is odd";
}
?>

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

Using ternary operator

php

<?php
$number = 7;
echo ($number % 2 == 0) ? "$number is even" : "$number is odd";
?>

This is a concise way to write the check and print in one line.

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

Time Complexity

The operation uses a single modulus calculation and a comparison, both constant time.

Space Complexity

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

Which Approach is Fastest?

Both modulus and bitwise AND methods run in constant time; bitwise may be slightly faster but less readable.

Approach	Time	Space	Best For
Modulus operator (%)	O(1)	O(1)	Readability and simplicity
Bitwise AND (&)	O(1)	O(1)	Performance in low-level operations
Ternary operator	O(1)	O(1)	Concise code