There are some occasions when you can use an affirmative structure and a rising intonation to ask a question. We do this to indicate surprise/ incredulity and to seek confirmation. For example, if you say 'My grandma swims three miles a day', I might reply by echoing your statement 'Your grandma swims three miles a day?' , stressing certain words to show my surprise and using an interrogative intonation to show that I want you to confirm this information.

Unfortunately, you do need to use the interrogative pattern in formal and informal speech and writing. You can choose the Spanish method of adding an inflection at the end of the sentence plus a "?" in informal speech, in 2 cases: when you are a) seeking re-assurance or b) casting doubt on something. (The inflection is not the same in both cases). In these cases, we often also add a tag question whereas Spanish has only "?no?" Because we do use the Spanish form in these specific situations, it's no problem for us to understand Spanish speakers when they use this form in every situation - it's just that it's wrong and you won't sound like an accomplished or professional speaker!