There are two ways to end a line of dialogue that isn’t meant to stand as a complete sentence.  One is with a dash, the other is with ellipses (those three spaced dots, remember?)

They aren’t interchangeable.

Ellipses are for utterances that trail off in some manner:

“Well,” she said, “if that’s what you really want . . . .” (That’s the ellipses, plus a period.)

“Well . . . if that’s what you really want, I suppose it’ll have to do.”  (That’s just the ellipses, showing how the speaker lets his or her voice trail off into a significant pause before going on to the rest of the sentence.

Dashes are for utterances that are broken off or are interrupted:

“I told you I wanted–”

“I know what you told me, but the store was all out of them.”


“And the winner is–”

(Drum roll.)

“Anastasia Oddfellow of East Drumstick, New Jersey!”

Got it?  Good.