Going for an interview? I've never seen a programmer pitch up for an interview without at least a tie and formal shirt/pants combination. That's the minimum, otherwise a suit.
Unless told otherwise you usually suit up. I remember once where I was told specifically not to suit up for an interview as they did not like suits(formality, they prefered hands on.. but then this was for engineering on coastal place in the middle of nowhere so yah wouldn't complain especially driving there lol)