I don’t know if this is what you’re asking, but if the input code has been written incorrectly, the output (the result) will be the same as the input code. And usually Mathematica will tell you what you did wrong. Example: PersonData[“BrianJacques, NotableBooks” the output would be: PersonData[“BrianJacques, NotableBooks” and then Mathematica would tell you that you didn’t type an ending right square bracket.

Hi Mac,

UnitConvert takes a Quantity as its first argument. Most units need to be specified as strings.

UnitConvert[Quantity[26.2, "Miles"], "Kilometers"]
CurrencyConvert[Quantity[10, "USDollars"], "Euros"]

Explore the documentation.

Hi Mac,

To expand a little on Eleazar's answer.

As a newcomer to WL it is important to understand that unlike most programming languages, WL uses term rewriting. When you define a function, you are actually defining a rewriting or replacement rule.

This defines a replacement where f[<something>] is replaced by <something>^2.

Clear[f, a, b]
f[x_] := x^2

f[2]
(* 4 *)
f[a + b]
(* (a + b)^2 *)

A replacement rule may also restrict the patterns to which it applies. This definition will only apply if the argument to f is an Integer. a + b is not an Integer so no replacement is performed (output = input).

Clear[f, a, b]
f[x_Integer] := x^2

f[2]
(* 4 *)

f[a + b]
(* f[a + b] *)

If you are interested in exploring this aspect of the language further, read this post and the many links it references.