These expressions are not particularly interesting. More complex (and
interesting) expressions can be created by combining simple
expressions. For example, we saw that `1.7` is an
expression and `i` is an expression. The following
is also an expression:

i + 1.7

The value of this expression is determined by adding the values of
the two simpler expressions. The `+` in this example
is an *operator* that is used to combine two
expressions into a more complex expression. Another operator is
`-`, which is used to combine expressions by
subtraction. For example:

(i + 1.7) - sum

This expression uses the `-` operator to subtract
the value of the `sum` variable from the value of
our previous expression, `i + 1.7`. JavaScript
supports a number of other operators besides `+` and
`-`, as you'll see in the next section.