You’ve got two options if you want to write "one hundred and fifty-six in French: You could just use the numbers like you would in English and write "156", or you could write it out in full as “cent cinquante-six.”
Pronunciation
“Cent cinquante-six” is pronounced so(n) sank-ont seece.
We tend to speak pretty fast in France, at least compared to the UK and the States, but clarity is more important than speed – especially when you’re not speaking your native language. Start by speaking clearly, and speed will soon follow!
Don't worry about articles like "le" or "un" - you don't need them for this. Whereas "hundred" in English would need an article, "cent" in French doesn't need one.