Numbers

Ruby has two main number types: Integer for whole numbers and Float for numbers with a decimal point.

Syntax

count = 42
price = 9.99
population = 8_100_000_000   # underscores are just for readability

Integers have no size limit — Ruby grows them as needed, so 2 ** 100 just works.

Example

puts 7 + 2
puts 7 - 2
puts 7 * 2
puts 7 / 2
puts 7 % 2
puts 7 ** 2
puts 7 / 2.0
puts 7.fdiv(2)
puts 10.0 / 3
puts (10.0 / 3).round(2)

Expected output

9
5
14
3
1
49
3.5
3.5
3.3333333333333335
3.33

Line by line:

• 7 / 2 is 3, not 3.5. When both numbers are integers, / does integer division and drops the remainder.
• % (modulo) gives the remainder: 7 % 2 is 1. It's handy for checking whether a number is even.
• ** raises to a power.
• If either side is a Float, the result is a Float. fdiv always returns a Float.
• Floats are approximate: 10.0 / 3 shows the tiny rounding error built into how computers store decimals. Use round(2) for display.

Numbers are objects with useful methods:

p -5.abs
p 10.even?
p 3.7.floor
p 3.2.ceil
p 17.clamp(1, 10)

5
true
3
4
10

Common mistakes

• Expecting 7 / 2 to be 3.5. Make one side a float (7 / 2.0) or use fdiv.
• Using Float for money. 0.1 + 0.2 is 0.30000000000000004. For money, store whole cents as integers (1999 for $19.99), or use the BigDecimal library.

Practice

A pizza has 8 slices shared by 3 people. Print how many whole slices each person gets, and how many are left over.

slices = 8
people = 3
puts slices / people
puts slices % people

2
2