Floating Point Numbers

If you expect someone to type a floating point value you can turn the String you get from IO.readln into a double using Double.parseDouble.

void main() {
    String gpaString = IO.readln("What is your GPA? ");
    double gpa = Double.parseDouble(gpaString);
    IO.println("You're GPA is " + gpa);
}

So long as they type something which can be interpreted as a double (like 123 or 14.5) you will get a value for the double variable. Otherwise the program will crash.