Comparison Operators

The symbols > and < are comparison operators: they compare two values. Lua has six of them:

• == equal to: 5 == 5
• ~= not equal to: 5 ~= 3
• > greater than: 5 > 3
• < less than: 3 < 5
• >= greater than or equal to: 5 >= 5
• <= less than or equal to: 3 <= 5

All the examples in the list are true. Watch the boundary: 12 > 12 is false, but 12 >= 12 is true. “A dozen eggs or more” is therefore eggs >= 12.

Every comparison gives a boolean, true or false, which you know from the previous lesson. You can print it, or store it in a variable:

local eggs = 12
print(eggs > 12, eggs >= 12)
local isDozen = eggs == 12
print("A dozen:", isDozen)

This prints:

false	true
A dozen:	true

In local isDozen = eggs == 12, Lua first compares and then stores the result. “Equal” is written with two equals signs, because one already has a job: eggs = 12 assigns (stores 12 in eggs), while eggs == 12 compares (asks whether eggs is 12, and changes nothing). A single = in a condition is a syntax error: if eggs = 12 then ends with 'then' expected near '='.

“Not equal” is ~= in Lua: a tilde and an equals sign. Many other languages write !=, which Lua doesn't know:

local day = "Monday"
if day != "Saturday" then
    print("No market today")
end

main.lua:2: 'then' expected near '!'

You can compare texts, too. Two texts are equal only if they match exactly, character by character: "Carrot" == "carrot" is false, because a capital letter is a different character. < and > compare texts in alphabetical order: "apple" < "banana" is true. All capital letters come before all lowercase ones, though, so "Zebra" < "apple" is true as well.

A number and a text are never equal, so 12 == "12" is false, even though Lua turns "10" + 5 into a number by itself. And <, >, <= or >= between a number and a text end with an error:

local eggs = "14"
if eggs < 12 then
    print("Not enough eggs")
end

main.lua:2: attempt to compare string with number

When a number comes as a text, convert it with tonumber first.