French language Q&A Forum

How do you say the following in French? 

a) I spent a day with Martin. 

b) I spent the day with Martin.

My guess is:

a) J’ai passé un jour avec Martin. (following the example of "spent a year" indirectly)

b) J’ai passé la journée avec Martin. (following the quiz answer directly)

Am I correct? If so, why are the two different? Can I just remember "a" vs. "the" means one is a unit of time and one is emphasizing the duration? Thank you. 

Bonjour Cécile. A few weeks ago I said I’d find an example of a run on sentence. In this lesson, I had one: Je ne peux pas parler maintenant, je suis en train de travailler. In English, we’d separate the two independent clauses with a semi-colon or a period, not a comma. I’m asking if it’s standard in French to use a comma to separate two clauses? Merci pour votre réponse !