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Modulo for dummies

by Antoine - Categories : Programming


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

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.

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

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