"Happy Birthday sir!" or "Happy Birthday, sir!"?

Which one is grammatically correct?

• Happy Birthday sir!
• Happy Birthday, sir!

And where should I put "sir" in this sentence?

• Congratulations for completing another trip around the sun!

Also suggest the position of the exclamation mark. Is it necessary or not?

Because you are addressing the subject ('sir') directly, you use a comma.

"Happy Birthday, sir!" is correct.

In the second question, you can simply add sir to the end and separate it with a comma:

"Congratulations for completing another trip around the sun, sir!"

As for whether the exclamation point is necessary, that depends entirely on one's relationship with the subject, as well as how momentous the occasion is. If one is friendly and relatively informal with the subject, the exclamation point is perfectly acceptable.

"Happy birthday, sir!" is correct.

When addressing someone directly, writers should separate the name/pronoun being used (e.g. Sir, Madam, John, Mary, honey, you little rascal, my son) from rest of the sentence using a comma or commas.