YOU SAID:
I have to go to the sandwich shop
INTO JAPANESE
私はサンドイッチ店に行かなければなりません
BACK INTO ENGLISH
I have to go to a sandwich shop
INTO JAPANESE
私はサンドイッチ店に行かなければなりません
BACK INTO ENGLISH
I have to go to a sandwich shop
That didn't even make that much sense in English.