how to use else lua code example

Example 1: elseif lua

if op == "+" then
      r = a + b
    elseif op == "-" then
      r = a - b
    elseif op == "*" then
      r = a*b
    elseif op == "/" then
      r = a/b
    else
      error("invalid operation")
    end

Example 2: lua if else

if bool then
	--code
else
	--code
end