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Modulo for dummies

The modulo is a mathematical operation useful as a programming operator when one needs to repeat an event every n times. Written «%»), the modulo actually returns the rest of an euclidean division.

A common application for it is to make a treatment for even iterations in a loop, and another one for odds. For example, this is can be useful for applying a conversation-like style in a comment flow like in my site. A "left to right" style is applied on odd iterations, and a "righ to left" on even iterations. But it can be useful for many other needs.

Examples

• 12 / 6 == 2, remains 0, so 12 % 6 == 0.

Another method, with the same operation, the goal is to "remove" as many times as possible "2" from the figure "7" to get as close as possible to zero : 7 -> 5 -> 3 -> 1 We can remove three times "2" from it, but we can't get lower than... 1, the remainder, and by the way the result of our modulo.

• 7 / 2 == 3, 1 remains, so 7 % 2 = 1

• Same method with 8 % 3 = 8 -> 5 -> 2

Code

PHP

$i = 0;
while ($i < 10) {
    $mod = $i % 3;
    echo $mod;
    $i++;
}

Ouput

0120120120

Python

Same example as above

i = 0
while (i < 10):
   mod = i % 3
   print(mod)
   i += 1

Python output

0
1
2
0
1
2
0
1
2
0

Another example

list = ["com1", "com2", "com3", "com4"]

for i in range(len(list)):          # Iterate over list indexes
   if i % 2 == 1:
         print(f'{list[i]} -> {i} % 2 -> 1 -> odd')
   else:
         print(f'{list[i]} -> {i} % 2 -> 0 -> even')

Python output

com1 -> 0 % 2 -> 0 -> even
com2 -> 1 % 2 -> 1 -> odd
com3 -> 2 % 2 -> 0 -> even
com4 -> 3 % 2 -> 1 -> odd