Exclamation points indicate emotion, an outcry, or a forceful comment. Try to avoid their use except in direct quotations and in rare and special circumstances. They are not appropriate in scientific manuscripts and are more common in less formal articles, such as book reviews, editorials, and informal essays, where added emphasis may be appropriate. If they are used, limit their use to one.
Although it may be referred to as the gold standard, nothing is perfect!
I had almost given up hope of his recovery. He was terribly sick!
When it completes the emphasized material, the exclamation point goes inside the end quotation mark, parenthesis, or bracket. (The exclamation point, like the question mark [see 8.1.2, Question Mark, Placement], is never combined with another exclamation point, question mark, period, semicolon, or comma; thus, there is no comma in the first example below.)
“Let the reader beware!” the editor warned.
The frightened child cried, “I don't want my tonsils taken out!”
In mathematical expressions, the exclamation point is used to indicate a factorial. (See 21.6, Mathematical Composition, Expressing Multiplication and Division.)
5! = 5 × 4 × 3 × 2 ×1