error C202 'P3_3' undefined identifier.. please tell me what changes to make in my program.

Isn't it obvious what to do when the code tries to reference an unknown symbol?

But you must figure out if you have spelled wrong or not written all required statements yet. Should be easy since you are expected to know the meaning of P3_3 (third bit on port P3???) If you don't, then your code is a partial cut/paste of code you don't understand, in which case you have bigger problems than just supplying all required definitions/declarations.

Isn't it obvious what to do when the code tries to reference an unknown symbol?

But you must figure out if you have spelled wrong or not written all required statements yet. Should be easy since you are expected to know the meaning of P3_3 (third bit on port P3???) If you don't, then your code is a partial cut/paste of code you don't understand, in which case you have bigger problems than just supplying all required definitions/declarations.