CSIT Class 6

Note: Scanner handout of last class is corrected: (position = 4 at the space, not past the space after “18.4” scanned, etc. (as shown on pg. 387)

P1 due next Tues: questions?

Q: How do we code the sum for #2

A:  The numbers to add are in arrays x[] and y[]. For the example, x[0] = 5, x[1] = 4, x[2] = 3, and x[3] = 2, y[0] = 9, and so on.

First do the addition with the numbers:

   2345

+ 9119

We add 5 and 9 and get 14, and put 4 in the sum and use the 1 for carry.

We add the carry of 1 plus 4 plus 1, and end up with result digit 6, carry = 0

..

Using array notation

x[0] + y[0] = 14:  sum[0] = 4 = 14 -10 or 14%10, carry = 1 = 14/10.

X[1] + y[1]  + carry = 6 = sum[1], carry = 0

…

In general, digit i:

s = x[i] + y[i]  + carry , sum[i] = s%10, carry =  s/10
 Make a loop with this body

Demo on using the new Wiki

Follow the link on the class web page to the Wiki, then find Programming Project 1 listed on the right-hand side and click it, then see a button at the top for posts and click it, read posts and/or post a new question.

Major example in Chap 8, on p1: Point objects.

Class Demo

Type in PointExample.java, pg. 505,with “import java.awt.*” to get the JDK Point class. (PointExample.java is not available online)

Add a Scanner on a String and print it out too, see position changing (its radix not reported, unfortunately)

       Scanner input = new Scanner("ab 123");       

       System.out.println(" input Scanner = " + input);  // see position = 0

       String s = input.next();

       System.out.println(" after input.next(), s = " + s  + " input = " + input); // see position = 2

This uses the Point class from the JDK, and this requires the import you see on line 1 on pg. 505.

  Point p = new Point(3,8);   // Point constructor call

  Compare to

   Scanner in = new Scanner(“ab cd”);  // Scanner constructor call

System.out.println(“initially p = “ + p);  // this is asking for p to provide a String to describe it, which is then printed out.

Similarly we can print out the internal state of a Scanner by asking for a String from it.

Not all object classes do a good job at this. For example arrays are objects, but don’t provide useful Strings for output.

But it’s often worth a try for debugging with various JDK classes.

Class Exercise: get started on p1 #3: 

Print the point’s x coordinate as a bar:

Ex Point at (5,1), print “-----“  5 hyphens