How to say != 0-9 in c ++ [duplicate]

Answer 1

For the C++ answer, look at this question which has already solved a quite similar problem, that you can very easily adapt to your situation.

As for Java, you can do this :

public boolean isInteger(String s) {
    return s.matches("^[0-9]+$");
}

You can modify the regex to suite your requirements. For example : "^[4-8]+$".

Note: String.matches is not optimal. If you need to perform checks often, use a compiled pattern instead :

static final Pattern DIGITS = Pattern.compile("^[0-9]+$");

public void isInteger(String s) {
    return DIGITS.matcher(s).find();
}