Values, types, and truth

The idea

Lua values carry types, while a variable can refer to values of different types over its lifetime. Common types include nil, boolean, number, string, table, and function. A variable without an assigned value has nil. Use local declarations for ordinary working variables so their names remain within the intended scope. Numbers support arithmetic, and the concatenation operator .. joins strings into a result.

Only false and nil are false in a condition. Zero and the empty string are both true, which matters when translating an algorithm from another language. The operators and and or return selected operands rather than converting every result to a boolean. A fallback using or therefore replaces false as well as nil; use an explicit nil check when false is meaningful input.

local count = 0
local label = ""
if count then print("zero is true") end
if label then print("empty is true") end
print("Items: " .. (3 + 2))

zero is true
empty is true
Items: 5

Both conditions succeed because their values are neither false nor nil. Parentheses make the arithmetic happen before the result is concatenated.