Did Roald Dahl use figures of speech in Charlie and the Chocolate Factory?
Most definitely. Figures of speech are comparitive literary devices that are used by nearly all authors to describe and explain. You might want to consider how Dahl presents characters and uses figures of speech to paint humorous pictures of them and suggest their characteristics. One of my favourites in this great novel is in Chapter Six, when we are introduced to the first winner of the Golden Ticket, Augustus Gloop. Consider how he is presented:
Great flabby folds of fat bulged out from every part of his body, and his face like a monstrous ball of dough with two small greedy curranty eyes peering out upon the world.
Note here how his face is compared to a "monstrous ball of dough" with a simile, suggesting his face looks like a massive ball of uncooked bread. Likewise a metaphor is used to compare his eyes to currants, emphasising his greed and suggesting that he really is not a pleasant character at all. Dahl's figures of speech are always exaggerations of character appearances and traits that are immensely amusing to identify and analyse. Hopefully this example will help you find others. Consider other descriptions of characters.