how to make else if statement in 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: if statement lua

if (conditon) then
	--action #1
elseif (condition) then
	--action #2
else
	--action #3
end