The modulo operator

Out of all operators in programming, it is the modulo operator that goes under the radar most. Perhaps this is due to a lack of need or even an understanding of how it works and when to use it.

In the simplest terms, modulo operator is the remainder from a division of one number by another. Compare this to a simple division which is the times the number goes into the other.

Examples

Here are some examples in PHP

echo (20 % 12);//8

The answer is 8 because 12 goes into 20 once and 8 is left over.

echo (40 % 12);//4

12 goes into 40 three times (36) and 4 is the remainder.

Checking if a number is odd or even with the modulo operator:

if ($number % 2 == 0) {
    echo "Even";
} else {
    echo "Odd";
}

This works because 2 will always go into an even number and have 0 remaining.

Another great use for the modulo operator is running a loop and getting every tenth, hundred, thousandth etc;

for ($i = 1; $i <= 100000; $i++) {
    if ($i % 5000 == 0) {
        echo $i.'<br>';
    }
}

Outputs

Whilst

for ($i = 1; $i <= 50000; $i++) {
    if ($i % 1500 == 0) {
        echo $i.'<br>';
    }
}

outputs