Difference between what a and such a

Question

I wonder, is it like one can use “What a nice day” as a sentence, independently, but has to include a verb in a sentence if he wants to say “Such a nice day.”Instead he may say It’s such a nice day.

What’s the difference?

Answer 1

Both are casual or conversational, mild intensifiers. There is no discernable difference in meaning.

There is some difference in use. "What" goes at the start of sentence, so you can say "What nice weather we are having!" or "Such nice weather we are having". But you can also so "We've had such nice weather". But you couldn't say "We've had what nice weather."

"What a nice day!" can be an exclamation standing as an independent sentence, whereas 'such a' requires a verb, even if it's only "It's such a nice day!" However in casual conversation, it might be implied.