Could you, please, help me out with this sentence
Your dad's bought a car, that's great
Is it correct to use comma before "that"? Would it be better if I separate those 2 halves with a full stop?
Thanks in advance.
As it's written, your sentence is the equivalent of separating two independent clauses with a comma. That's known as a comma splice. While a comma splice is acceptable in some situations, I wouldn't say this is one of them.
There are multiple ways you can deal with this.
1. You can explicitly separate the sentence into two independent clauses with different punctuation:
Your dad's bought a car. That's great.
Your dad's bought a car; that's great.
Your dad's bought a car—that's great.
2. You can turn the second part of the sentence into a clarifying term for the first part with a colon:
Your dad's bought a car: that's great.
3. You can use a comma followed by a conjunction:
Your dad's bought a car, and that's great.
4. You can use a comma but turn what follows it into a nonrestrictive clause:
Your dad's bought a car, which is great.
Note that this leaves the meaning of the sentence ambiguous. It's not clear if it's the fact that he bought a car that's great or if it's the car itself that's great.
5. You can eschew punctuation altogether but make what currently follows it into a restrictive clause:
Your dad's bought a car that's great.
Here, it's clear that it's the car itself that's great, not his purchase of it.
Some of these variations are simply a matter of preference, while others are determined by the exact meaning of what you're trying to convey.