The Modulo Operator in Swift: Finding Remainders with %

TL ; DR:

• The modulo operator (%) calculates the remainder of dividing two values:

  print(10 % 2) // Output: 0
  print(15 % 4) // Output: 3
  print(20 % 3) // Output: 2
  

  
  

• It can also be used with variables:

  var a = 2
  var b = 4
  
  print(b % a) // Output: 0
  print(11 % b) // Output: 3
  

Full lesson:

Remember how we first learn about the division of two integer numbers in primary school?

The quotient is the number of times a division is completed fully, while the remainder is the amount left that doesn't entirely go into the divisor.

Here are some examples:

10 / 2 = quotient 5, remainder 0
15 / 4 = quotient 3, remainder 3
20 / 3 = quotient 6, remainder 2

The modulo operator:

The modulo operator (%) calculates the remainder of dividing two values:

print(10 % 2) // Output: 0
print(15 % 4) // Output: 3
print(20 % 3) // Output: 2

It can also be used with variables:

var a = 2
var b = 4

print(b % a) // Output: 0
print(11 % b) // Output: 3

floor() function

The floor() function returns the largest integer less than or equal to a given number (it needs import Foundation and returns a Double, so we wrap it in Int(...)):

import Foundation

print(Int(floor(3.9))) // Output: 3
print(Int(floor(5.2))) // Output: 5
print(Int(floor(7.0))) // Output: 7

We can use this function if we want to compute the integral part of some division (quotient):

var a = 2
var b = 3

var c = b / a
print(c) // Output: 1

Quotient and remainder:

In programming, we combine both these concepts to get the quotient and remainder of some division:

// Let's divide 26 by 3:
var quotient = 26 / 3
var remainder = 26 % 3

print(quotient) // Output: 8
print(remainder) // Output: 2

Assignment
Follow the Coding Tutorial and let's practice with quotient and remainder!

Hint
Look at the examples above if you get stuck.