Returning a value

Functions don't just take input, they can also return some output to the calling code. This is done through a return value. When a function returns a value, it can be called as part of an expression or as a standalone statement.

If a function is called as a part of an expression, its return value can be assigned to a variable, or used wherever a variable could be used. The following code demonstrates this concept:

-- declare the function
function AddTwo(x)
  result = x + 2
  print (x .. " + 2 = " .. result)
  return result
end

AddTwo(3) -- calls as statement
nine = 7 + AddTwo(5) -- Call as expression
print ("adding two " .. AddTwo(3)) -- Call as expression

When a function hits a return statement, it returns whatever data follows and stops executing. If you have code after your return statement, that code will not execute, for example:

-- Declare the function
function SquareIt(number)
  result = number * number
  print ("this will print") -- WILL PRINT!
  do
    return result
  end
  print ("this will not print") -- WILL NOT PRINT
end

-- Call the function
four = SquareIt(2) -- Will print: this will print
print(four) -- Will print: 4