CS115 lecture notes, Spring 1999
Week 11, Monday


Hand back exams.

Reading: Chapter 10

	 Warning: lots of errors in this Chapter.

Quiz Wednesday on arrays.


Arrays
------

An array is a set or collection of values, sort of like an
objects, except:

  All the values have the same type.

  The values are indicated by number, rather than name.

For every primitive type, there is a corresponding array
type:

	int	int[]	  (array of int)
	double	double[]  (array of double)

You can declare array variables in the usual way:

    int[] count;
    double[] doubleArray;

Just as with objects, these declarations create references
to arrays.  To allocate space for the array itself, you have
to use the new command:

   count = new int[4];
   doubleArray = new double[size];

The number in the square brackets is the size of the array.

It can be any integer expression.

By default, the elements of the array are initialized to zero.


Elements of an array
--------------------

The elements are numbered from zero.

count[0] = 7;
count[1] = count[0] * 2;
count[2]++;
count[3] = count[3] - 60;

You can use any integer expression as an index.

If you use an index that is negative or >= size, you get
an ArrayOutOfBoundsException.

You can use loops to traverse arrays:

    int i = 0;
    while (i<4) {
      System.out.println (count[i]);
      i++;
    }

Example:

Given an array of doubles, a, how would you make a copy?

  double[] a = new double[3];
  double[] b = a;

This copies a reference to the array, which means that
a and b are now aliased.

To build a new array, we have to use new to allocate
space, and a loop to copy the elements of the array.

    double[] b = new double [3];

    int i = 0;
    while (i < 4) {
      b[i] = a[i];
      i++;
    }