Examine and study each example carefully. Predict about what each example will do when it runs. Your prediction should be included as comments to the code (#).

Modulo (usually just called mod) performs integer division and returns the remainder only.

It uses the % operator.

For example:

3 % 1 = 3 remainder 0, so the value returned would be 0.

5 % 2 = 2 remainder 1, so the value returned would be 1.

14 % 4 = 3 remainder 2, so the value returned would be 2.

Modulo is really useful for working out whether a number is divisible by another one – if the remainder returned is 0 then the number is exactly divisible.

So to calculate if a number isodd or even you would mod it by 2, if the remainder is 0 then the number is even. ex:

remainder = num % 2
if remainder == 0:
  print("Even number")
else:
  print("Odd number")

Modulo can be used in conditions – better students may do this, but I make them do it the ‘long way round’ and assign the result to a variable until I’m happy that they have a solid understanding of the skill.

For example, the code above could also be written like this:

if num % 2 == 0:
  print("Even number")
else:
  print("Odd number")

This removes the need for the vairable and makes the code shorter, but more syntactically dense and harder do undersatnd for new coders.

At the ‘predict’ & ‘run’ stages students work entirely with example code. They should inspect it carefully and write a prediction about what it will do.

They then run the code and compare the result to their prediction.

Make sure to check your code for the following mistakes:

• use a single % as the operator
• a number or number variable either side of the operator
• assign the remainder to a variable (or better students may use it straight in a condition)