How is hypnotherapy different than affirmations?

Hypnotherapy has the advantage of being able to communicate with the subconscious immediately and affirmations have to be repeated consistently for a period of time till the subconscious accepts them as suggestions.

A post-hypnotic suggestion is also different than an affirmation: effects tend to be more direct, more specific, and more immediate when using post-hypnotic suggestions.

Other than that, the language of hypnosis and of affirmations is similar as both focus on positive lasting changes. 

Will you make me bark like a dog or cluck like a chicken?

Would you want me to ?? You probably have seen shows or experienced stage hypnosis where a hypnotist made people do all these crazy 

Hypnosis can not make you do something that is against your morals or ethics. All hypnosis is self-hypnosis, in truth, and no hypnotist can make you do something that you really don't want to . You have to really want the change, agree with the change, and then hypnosis is an instrument for helping make that change better, faster, and permanent. Your free will can  never be compromised during hypnosis.

What can't be treated with hypnotherapy?

Serious psychiatric or mental health problems are referred to a qualified psychotherapist or psychiatrist. Medical problems with the physical body must always be treated by a physician, who can, at his or her discretion, prescribe hypnotherapy for pain control, hypnoanesthesia or relaxation.

Drug addiction, family dynamics disorders, clinical depression and other such problems need to be treated by doctors and psychiatrists, who can, at their discretion, prescribe hypnotherapy as a supplementary treatment.