## 17.1 Example - Operator Functions

- The difference between two `Time` objects is the number of seconds between them

  >     int operator-( Time a, Time b )
  >     {
  >        return a.seconds_from( b );
  >     }

- Use the `-` operator instead of calling `seconds_from()`:

  >     Time now;
  >     Time morning( 9, 0, 0 );
  >     int seconds_elapsed = now - morning;

- `operator-` is a nonmember function with two parameters

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