"In the army you ......... (have to/must) Wear uniform "
Someone insisted its "have to" not "must" is that right?

Question

Answer

Either of those are correct.
In the army you have to wear a uniform.
In the army you must wear a uniform.

Answer

Probably "have to" would be most accurate.  It implies that it is a rule and that the order comes from above you and you have no choice. "Must" is logical deduction or personal circumstance that makes something necessary.  See article.: http://www.englishgrammarsecrets.com/musthaveto/menu.php

Hope that helps.

Answer

"In the army you have to wear a uniform."

Stephanie's link explains it well. Take note of the "personal circumstance / external circumstance" guideline and this will solve the dilemma.