What is the difference between いえ、けっこです。 and いえ、大丈夫です。 and also for example in a convience store if they ask you if they should heat the food, which of thes... ?

3 Dec 2014

Native language
German
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Question about Japanese
What is the difference between いえ、けっこです。 and いえ、大丈夫です。 and also for example in a convience store if they ask you if they should heat the food, which of these denied answer sounds more natural? also is いえ before ok or would you leave it out??
Feel free to just provide example sentences.