Student or Learner
When you want to compliment someone about his/her back being nice and straight using the word 'posture', do you say "You have a good posture." or "You have good posture."?
And how about in case of saying not having straight back, would it be "You have a bad posture." or "You have bad posture."?
You have (got) good/bad posture.
My cousin-brother insists on slouching.