What is the difference between 4 and 4.?

Merely adding a decimal point after a number does not change its value, and in fact it should be omitted, unless one or more digits follow. For example, "4.0" indicates that the number is accurate to one additional decimal place, while "4.00" is accurate to two additional places, and so on (although the value is still 4). However, "4." (decimal point without any digits following) only makes sense at the end of sentence, thus the point should be removed.